Docs: fix space-before-blocks correct code for "classes": "never" (#1…

…1391)

Examples of **correct** code for this rule when configured `{ "functions": "never", "keywords": "always", "classes": "never" }`:

Replaced
```js
class Foo {
  constructor(){}
}
```
with
```js
class Foo{
  constructor(){}
}
```

docs/rules/space-before-blocks.md

@@ -143,7 +143,7 @@ describe(function(){
   // ...
 });
 
-class Foo {
+class Foo{
   constructor(){}
 }
 ```