[1.0] Fix windows paths (gatsbyjs#781)

* Fix component path in gatsbygram/createPages

* Fix component path into gatsby-plugin-offline

* Fix path comparaison on query-runner watcher

* Refactor promise pattern

It's really hard to read with outsideResolve ;)

* Remove unused variables

* Fix path on gatsby/bootstrap

* Fix paths on build-node-types

* Remove miscommit debug line

* Update sharp dependency

* Run `yarn format`

* Add windows docs

* Add gatsby-on-windows on Quick Start link

* Fix path on gatsby-source-filesystem

* Fix www project on windows

* Fix responsive image on windows

* Apply windows fix in gatsbygram-case-study doc

* Fix `fix-semi` command on windows

* Run `yarn format`

src/gatsby-node.js

@@ -74,7 +74,7 @@ exports.sourceNodes = ({ args, pluginOptions }) =>
                     sourceName: pluginOptions.name,
                     children: [],
                     relativePath: slash(
-                      path.posix.relative(pluginOptions.path, file.absolutePath)
+                      path.relative(pluginOptions.path, file.absolutePath)
                     ),
                     extension: file.ext.slice(1).toLowerCase(),
                     size: file.size,