fix(mp): add Reflect

packages/webpack-uni-mp-loader/lib/plugin/generate-app.js

@@ -62,7 +62,7 @@ module.exports = function generateApp (compilation) {
   ) {
     const source =
       `
-  !function(){try{var r=Function("return this")();r&&!r.Math&&Object.assign(r,{Array:Array,Date:Date,Error:Error,Function:Function,Math:Math,Object:Object,RegExp:RegExp,String:String,TypeError:TypeError,setTimeout:setTimeout,clearTimeout:clearTimeout,setInterval:setInterval,clearInterval:clearInterval})}catch(r){}}();
+  !function(){try{var a=Function("return this")();a&&!a.Math&&(Object.assign(a,{Array:Array,Date:Date,Error:Error,Function:Function,Math:Math,Object:Object,RegExp:RegExp,String:String,TypeError:TypeError,setTimeout:setTimeout,clearTimeout:clearTimeout,setInterval:setInterval,clearInterval:clearInterval}),"undefined"!=typeof Reflect&&(a.Reflect=Reflect))}catch(a){}}();
   ${compilation.assets[runtimeJsPath].source()}
   `
     compilation.assets[runtimeJsPath] = {