[WDS] Disconnected!

# Bug Report

**Ionic Info**
Run `ionic info` from a terminal/cmd prompt and paste the output below.

Ionic:

ionic (Ionic CLI) : 4.0.5 (/usr/lib/node_modules/ionic)
Ionic Framework : @ionic/angular 4.0.0-beta.1
@angular-devkit/core : 0.7.2
@angular-devkit/schematics : 0.7.2
@angular/cli : 6.1.2
@ionic/ng-toolkit : 1.0.5
@ionic/schematics-angular : 1.0.4

Cordova:

cordova (Cordova CLI) : 8.0.0
Cordova Platforms : android 7.0.0

System:

Android SDK Tools : 26.1.1
NodeJS : v8.11.3 (/usr/bin/node)
npm : 5.10.0
OS : Linux 4.4

Environment:

ANDROID_HOME : /home/woodz/Android/Sdk

**Describe the Bug**
the browser sometimes show the content sometimes show totally the blank page when reload.
Furthermore, the inspect error show:
[WDS] Disconnected! vendor.js:91813:5
close
http://localhost:8100/vendor.js:91813:5
onclose
socket.js:17
./node_modules/sockjs-client/dist/sockjs.js/

先使用新的 Angular 專案和 `ionic serve` 重現問題，然後檢查 `vendor.js` 和 `socket.js` 中的 `[WDS] Disconnected!` 追蹤資訊。當重新載入不再間歇性地產生空白頁面，且中斷連線行為有回歸測試涵蓋時，工作即告完成。

由索引模型根據 Issue 內容生成。