make sure esModule is always true in inject mode

Author: yyx990803

lib/loader.js

@@ -50,8 +50,15 @@ module.exports = function (content) {
   var loaderContext = this
   var query = loaderUtils.getOptions(this) || {}
   var options = Object.assign({
-    esModule: !query.inject
+    esModule: true
   }, this.options.vue, this.vue, query)
+
+  // disable esModule in inject mode
+  // because import/export must be top-level
+  if (query.inject) {
+    options.esModule = false
+  }
+
   // #824 avoid multiple webpack runs complaining about unknown option
   Object.defineProperty(this.options, '__vueOptions__', {
     value: options,