message: refactor: use util.isNative to check native Proxy
diff: /* not type checking this file because flow doesn't play well with Proxy */
  import config from 'core/config'
  -import { warn, makeMap } from '../util/index'
  +import { warn, makeMap, isNative } from '../util/index'
  let initProxy
  @@ -25,8 +25,7 @@ if (process.env.NODE_ENV !== 'production') {
  }
  const hasProxy =
  - typeof Proxy !== 'undefined' &&
  - Proxy.toString().match(/native code/)
  + typeof Proxy !== 'undefined' && isNative(Proxy)
  if (hasProxy) {
  const isBuiltInModifier = makeMap('stop,prevent,self,ctrl,shift,alt,meta,exact')
  