[build] Upgrade to vue-cli 4

Author: g3force

babel.config.js

@@ -1,5 +1,5 @@
 module.exports = {
     presets: [
-        '@vue/app'
+        '@vue/cli-plugin-babel/preset'
     ]
 };

package.json

@@ -9,16 +9,16 @@
     "genProto": "pbjs -t static-module -w es6 -o src/sslProto.js src/proto/*.proto"
   },
   "dependencies": {
-    "core-js": "^2.6.5",
+    "core-js": "^3.4.4",
     "protobufjs": "^6.8.8",
     "vue": "^2.6.10",
     "vue-native-websocket": "^2.0.13",
     "vuex": "^3.1.1"
   },
   "devDependencies": {
-    "@vue/cli-plugin-babel": "^3.8.0",
-    "@vue/cli-plugin-eslint": "^3.8.0",
-    "@vue/cli-service": "^3.8.0",
+    "@vue/cli-plugin-babel": "^4.1.2",
+    "@vue/cli-plugin-eslint": "^4.1.2",
+    "@vue/cli-service": "^4.1.2",
     "babel-eslint": "^10.0.1",
     "eslint": "^5.16.0",
     "eslint-plugin-vue": "^5.0.0",