avoid multiple webpack runs complaining about unknown option (fix #824)

Author: yyx990803

lib/loader.js

@@ -49,9 +49,15 @@ module.exports = function (content) {
 
   var loaderContext = this
   var query = loaderUtils.getOptions(this) || {}
-  var options = this.options.__vueOptions__ = Object.assign({}, this.options.vue, this.vue, query)
-  var rawRequest = getRawRequest(this, options.excludedPreLoaders)
+  var options = Object.assign({}, this.options.vue, this.vue, query)
+  // #824 avoid multiple webpack runs complaining about unknown option
+  Object.defineProperty(this.options, '__vueOptions__', {
+    value: options,
+    enumerable: false,
+    configurable: true
+  })
 
+  var rawRequest = getRawRequest(this, options.excludedPreLoaders)
   var filePath = this.resourcePath
   var fileName = path.basename(filePath)