fix: fix inconsistent hashes between Windows and POSIX systems (#28)

Author: sharkykh

Diff for: index.js

@@ -18,7 +18,8 @@ module.exports.pitch = function (remainingRequest) {
   var addStylesShadowPath = loaderUtils.stringifyRequest(this, '!' + path.join(__dirname, 'lib/addStylesShadow.js'))
 
   var request = loaderUtils.stringifyRequest(this, '!!' + remainingRequest)
-  var id = JSON.stringify(hash(request + path.relative(__dirname, this.resourcePath)))
+  var relPath = path.relative(__dirname, this.resourcePath).replace(/\\/g, '/')
+  var id = JSON.stringify(hash(request + relPath))
   var options = loaderUtils.getOptions(this) || {}
 
   // direct css import from js --> direct, or manually call `styles.__inject__(ssrContext)` with `manualInject` option