fix: ensure consistent component id on different OS

ref: vuejs/vue-cli#1728

Author: yyx990803

Diff for: lib/index.js

@@ -67,7 +67,8 @@ module.exports = function (source) {
   // module id for scoped CSS & hot-reload
   const shortFilePath = path
     .relative(context, resourcePath)
-    .replace(/^(\.\.[\\\/])+/, '') +
+    .replace(/\\/g, '/')
+    .replace(/^(\.\.\/)+/, '') +
     resourceQuery
 
   const id = hash(