fix(mp-alipay): 修复 使用 $emit 触发事件报错的Bug

packages/vue-cli-plugin-uni/packages/mp-vue/dist/mp.runtime.esm.js

@@ -5827,9 +5827,10 @@ function internalMixin(Vue) {
 
   Vue.prototype.$emit = function(event) {
     if (this.$scope && event) {
-      (this.$scope['_triggerEvent'] || this.$scope['triggerEvent'])(event, {
+      (this.$scope['_triggerEvent'] || this.$scope['triggerEvent'])
+        .call(this.$scope, event, {
           __args__: toArray(arguments, 1)
-      });
+        })
     }
     return oldEmit.apply(this, arguments)
   };