Ionic serve launches browser to "Invalid Host header" only

# Bug Report

**Ionic Info**

```
Ionic:

ionic (Ionic CLI) : 4.0.1 (/home/david/.nvm/versions/node/v9.11.2/lib/node_modules/ionic)
Ionic Framework : @ionic/angular 4.0.0-beta.0
@angular-devkit/core : 0.7.0-rc.3
@angular-devkit/schematics : 0.7.0-rc.3
@angular/cli : 6.0.8
@ionic/ng-toolkit : 1.0.0
@ionic/schematics-angular : 1.0.1

System:

NodeJS : v9.11.2 (/home/david/.nvm/versions/node/v9.11.2/bin/node)
npm : 5.6.0
OS : Linux 4.14
```

**Describe the Bug**

In a new Ionic v4 beta project when I simply run `ionic serve` it launches a browser but only displays the message "Invalid Host header" as the only page content.

**Steps to Reproduce**
Steps to reproduce the behavior:

(Follow exact steps in docs for a new v4 beta project.)

1. `npm install -g ionic`
2. `ionic start myApp tabs --type=angular`
3. `ionic serve`
4. See error in browser

**Related Code**

N/A

**Expected Behavior**

That it launches the app content in the browser.

**Additional Context**

I'm on a Pixelbook so running inside a LXC container so this issue might be limited to containers.

Maybe a workaround would be to configure webpack to work with the Chrome OS Linux LXC container (aka Crostini) default hostname of `penguin.linux.test`?

首先，在回報的環境中使用 `ionic start myApp tabs --type=angular`，接著執行 `ionic serve`，重現此問題。閱讀 Ionic CLI 的 serve 路徑及其 webpack 設定，然後驗證瀏覽器顯示的是應用程式內容，而不是 `Invalid Host header`。

由索引模型根據 Issue 內容生成。