fix(build): fix generated code containing unprocessed class field syntax

fix #4052
fix vuejs/vue-cli#6562

tsconfig.json

@@ -3,7 +3,8 @@
     "baseUrl": ".",
     "outDir": "dist",
     "sourceMap": false,
-    "target": "esnext",
+    "target": "es2016",
+    "useDefineForClassFields": false,
     "module": "esnext",
     "moduleResolution": "node",
     "allowJs": false,