fix: fix ssr env detection in weex (vuejs#7375)

Author: Hanks10100

src/core/util/env.js

@@ -38,7 +38,7 @@ let _isServer
 export const isServerRendering = () => {
   if (_isServer === undefined) {
     /* istanbul ignore if */
-    if (!inBrowser && typeof global !== 'undefined') {
+    if (!inBrowser && !inWeex && typeof global !== 'undefined') {
       // detect presence of vue-server-renderer and avoid
       // Webpack shimming the process
       _isServer = global['process'].env.VUE_ENV === 'server'