Rename spec/built_in_modules -> spec/built-in-modules (#3051)

This matches the hyphen-separated style of other files and directories
in spec/.

accepted/angle-units.md

@@ -135,7 +135,7 @@ Because `hsla()` is identical to `hsl()`, it's updated identically.
 
 In the four-argument overload of [`color.hwb()`], replace
 
-[`color.hwb()`]: ../spec/built_in_modules/color.md#hwb
+[`color.hwb()`]: ../spec/built-in-modules/color.md#hwb
 
 * If `$hue` has any units other than `deg`, throw an error.
 
@@ -172,14 +172,14 @@ adjust-hue($color, $degrees)
 * Return the result of calling [`hsl()`] with `degree`, `saturation`,
   `lightness`, and `$color`'s alpha channel.
 
-[`color.saturation($color)`]: ../spec/built_in_modules/color.md#saturation
-[`color.lightness($color)`]: ../spec/built_in_modules/color.md#lightness
+[`color.saturation($color)`]: ../spec/built-in-modules/color.md#saturation
+[`color.lightness($color)`]: ../spec/built-in-modules/color.md#lightness
 
 ### `color.adjust()`
 
 In the definition of [`color.adjust()`], after
 
-[`color.adjust()`]: ../spec/built_in_modules/color.md#adjust
+[`color.adjust()`]: ../spec/built-in-modules/color.md#adjust
 
 * If `$hue` isn't a number or null, throw an error.
 
@@ -249,7 +249,7 @@ or `$lightness` parameters to `hsl()`, `hsla()`, `color.adjust()`, or
 warning.
 
 [`hsla()`]: ../spec/functions.md#hsl-and-hsla
-[`color.change()`]: ../spec/built_in_modules/color.md#change
+[`color.change()`]: ../spec/built-in-modules/color.md#change
 
 > Unitless hues should not cause deprecation warnings, but unitless saturations
 > and lightnesses should.

accepted/color-4-hwb.md

@@ -134,7 +134,7 @@ All new functions are part of the `sass:color` built-in module.
 
   * Return a color with the given `red`, `green`, `blue`, and `alpha` channels.
 
-  [percent-converting]: ../spec/built_in_modules/color.md#percent-converting-a-number
+  [percent-converting]: ../spec/built-in-modules/color.md#percent-converting-a-number
   [to RGB]: https://www.w3.org/TR/css-color-4/#hwb-to-rgb
 
 

accepted/more-math-functions.md

@@ -71,7 +71,7 @@ preferred value in between the minimum and maximum values, while preserving
 their units appropriately. For example, `clamp(1in, 15cm, 12in)` outputs `15cm`,
 whereas `clamp(1in, 1cm, 12in)` outputs `1in`.
 
-[compatible]: ../spec/built_in_modules/math.md#compatible
+[compatible]: ../spec/built-in-modules/math.md#compatible
 
 `hypot()` accepts `n` SassScript numbers with compatible units, and outputs the
 length of the `n`-dimensional vector that has components equal to each of the

accepted/slash-separator.md

@@ -357,7 +357,7 @@ overload to be the following:
 This proposal modifies [the "Parse a Selector From a SassScript Object"
 procedure][] to throw an error whenever it encounters a slash-separated list.
 
-[the "Parse a Selector From a SassScript Object" procedure]: ../spec/built_in_modules/selector.md#parse-a-selector-from-a-sassscript-object
+[the "Parse a Selector From a SassScript Object" procedure]: ../spec/built-in-modules/selector.md#parse-a-selector-from-a-sassscript-object
 
 ### Slash-Free Numbers
 

proposal/first-class-calc.md

@@ -363,8 +363,8 @@ This algorithm takes a calculation `calc` and returns a number or a calculation.
   arguments.
 
   [compatible]: ../spec/types/number.md#compatible-units
-  [`math.min()`]: ../spec/built_in_modules/math.md#min
-  [`math.max()`]: ../spec/built_in_modules/math.md#max
+  [`math.min()`]: ../spec/built-in-modules/math.md#min
+  [`math.max()`]: ../spec/built-in-modules/math.md#max
 
 * Otherwise, return a calculation with the same name as `calc` and `arguments`
   as its arguments.
@@ -515,7 +515,7 @@ To evaluate a `CalcValue` production `value` into a `CalculationValue` object:
 Add the following clause to the [`meta.type-of()`] function and the top-level
 `type-of()` function:
 
-[`meta.type-of()`]: ../spec/built_in_modules/meta.md#type-of
+[`meta.type-of()`]: ../spec/built-in-modules/meta.md#type-of
 
 * If `$value` is a calculation, return `"calc"`.
 

spec/functions.md

@@ -112,8 +112,8 @@ adjust-hue($color, $degrees)
   `lightness`, and `$color`'s alpha channel.
 
 [`hsl()`]: #hsl-and-hsla
-[`color.saturation($color)`]: built_in_modules/color.md#saturation
-[`color.lightness($color)`]: built_in_modules/color.md#lightness
+[`color.saturation($color)`]: built-in-modules/color.md#saturation
+[`color.lightness($color)`]: built-in-modules/color.md#lightness
 
 ### `alpha()`
 
@@ -168,7 +168,7 @@ plain CSS function named `"rgb"` that function is named `"rgba"` instead.
 
   * Return a color with the given `red`, `green`, `blue`, and `alpha` channels.
 
-  [percent-converting]: built_in_modules/color.md#percent-converting-a-number
+  [percent-converting]: built-in-modules/color.md#percent-converting-a-number
 
 * ```
   rgb($red, $green, $blue)

spec/modules.md

@@ -139,10 +139,10 @@ member of any given type and name. It's always mutable.
 A *built-in module* is a module defined either by the Sass specification or by
 the host environment of the Sass compilation in some implementation-specific
 way. Modules defined by the Sass specification all have the scheme `sass:` and
-are all described in [the `built_in_modules` directory][]. Modules defined
+are all described in [the `built-in-modules` directory][]. Modules defined
 outside the Sass compilation may not use the scheme `sass:`.
 
-[the `built_in_modules` directory]: built_in_modules
+[the `built-in-modules` directory]: built-in-modules
 
 Built-in modules may contain mixins, variables, or functions, but they may never
 contain CSS or extensions.