fix: include query in loader dedupe

ref: vue-cli#2451

lib/loaders/pitcher.js

@@ -63,14 +63,19 @@ module.exports.pitch = function (remainingRequest) {
  // also make sure to dedupe based on loader path.
  // assumes you'd probably never want to apply the same loader on the same
  // file twice.
+ // Exception: in Vue CLI we do need two instances of postcss-loader
+ // for user config and inline minification. So we need to dedupe baesd on
+ // path AND query to be safe.
  const seen = new Map()
  const loaderStrings = []
 
  loaders.forEach(loader => {
- const type = typeof loader === 'string' ? loader : loader.path
+ const identifier = typeof loader === 'string'
+ ? loader
+ : (loader.path + loader.query)
  const request = typeof loader === 'string' ? loader : loader.request
- if (!seen.has(type)) {
- seen.set(type, true)
+ if (!seen.has(identifier)) {
+ seen.set(identifier, true)
  // loader.request contains both the resolved loader path and its options
  // query (e.g. ??ref-0)
  loaderStrings.push(request)