ionic serve --ssl does not work with angular 12

**Description:**
--ssl is broken with Angular 12

**Steps to Reproduce:**
```bash
ionic start myApp tabs --type=angular
ionic ssl generate
ionic serve --ssl
```

**Output:**
Server starts, however, browser shows error 504

**My `ionic info`:**

```
Ionic:

Ionic CLI : 6.16.3 (C:\nvm\v12.20.0\node_modules\@ionic\cli)
Ionic Framework : @ionic/angular 5.6.9
@angular-devkit/build-angular : 12.0.5
@angular-devkit/schematics : 12.0.5
@angular/cli : 12.0.5
@ionic/angular-toolkit : 4.0.0

Cordova:

Cordova CLI : not installed
Cordova Platforms : not available
Cordova Plugins : not available

Utility:

cordova-res : 0.15.3
native-run : 1.4.0

System:

NodeJS : v12.20.0 (C:\nodejs\node.exe)
npm : 6.14.8
OS : Windows 10
```

**Other Information:**

Running ```ionic serve``` without --ssl runs ok.

```bash
$ng version
_ _ ____ _ ___
/ \ _ __ __ _ _ _| | __ _ _ __ / ___| | |_ _|
/ △ \ | '_ \ / _` | | | | |/ _` | '__| | | | | | |
/ ___ \| | | | (_| | |_| | | (_| | | | |___| |___ | |
/_/ \_\_| |_|\__, |\__,_|_|\__,_|_| \____|_____|___|
|___/

Angular CLI: 12.0.5
Node: 12.20.0
Package Manager: npm 6.14.8
OS: win32 x64

Angular: 12.0.5
... cli, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router

Package Version
---------------------------------------------------------
@angular-devkit/architect 0.1200.5
@angular-devkit/build-angular 12.0.5
@angular-devkit/core 12.0.5
@angular-devkit/schematics 12.0.5
@schematics/angular 12.0.5
rxjs 6.6.7
typescript 4.2.4

```

Reproduce the issue with the listed ionic start, ionic ssl generate, and ionic serve --ssl commands using Angular 12 on Windows. Inspect the Ionic CLI serve and SSL integration with Angular's development server; done means HTTPS serves the generated application without the browser returning a 504.

由索引模型根据 Issue 内容生成。