You are trying to set "Companion" which is a final field!

Environment
Provide version numbers for the following components (information can be retrieved by running tns info in your project folder or by inspecting the package.json of the project:

CLI: 8.2.14
Cross-platform modules:
"tns-core-modules": "~6.5.15"
"nativescript-feedback": "^1.5.0",

Describe the bug
Calling this.feedback.show({..} ) fails with Error: You are trying to set "Companion" which is a final field! Final fields can only be read.

Add plugin into a new {N} project. Import and execute:

var test = require("nativescript-kotlintest");
test.doTest();

feedback.service.js :

```
import { Injectable } from '@angular/core';
import { Feedback, FeedbackType } from 'nativescript-feedback';

@Injectable({
providedIn: 'root'
})
export class FeedbackService {
private feedback: Feedback;

constructor() {
this.feedback = new Feedback();
}

showSuccessMessage(message: string) {
this.feedback.show({
message: message,
type: FeedbackType.Success
});
}
}
```

Component.ts:

```
login() {
this.processing = false;
this.authService.login(this.user.email, this.user.password).subscribe(
data => {
this.feedbackService.showSuccessMessage("test message");
this.routerExtensions.navigate(['/bills/tabs'], { clearHistory: true });
},
error => {
console.log(error);
}
);
}
```

Expected behavior
To not crash.

Additional context:
Issue occur if function gets invoked.

Full stacktrace:
```
JS: ERROR Error: Uncaught (in promise): Error: You are trying to set "Companion" which is a final field! Final fields can only be read.
JS: Error: You are trying to set "Companion" which is a final field! Final fields can only be read.
JS: at file:///node_modules/nativescript-feedback/feedback.js:17:0
JS: at new ZoneAwarePromise file:///node_modules/@nativescript/angular/zone-js/dist/zone-nativescript.js:902:0
JS: at Feedback.show file:///node_modules/nativescript-feedback/feedback.js:15:0
JS: at FeedbackService.module.exports.push../app/shared/services/feedback.service.ts.FeedbackService.showSuccessMessage file:///src/app/shared/services/feedback.service.ts:15:18
JS: at SafeSubscriber._next file:///src/app/auth/auth.component.ts:50:29
JS: at SafeSubscriber.push.../node_modules/rxjs/_esm5/internal/Subscriber.js.SafeSubscriber.__tryOrUnsub file:///node_modules/rxjs/_esm5/internal/Subscriber.js:192:0
JS: at SafeSubscriber.push.../node_modules/r...
```

Further github issue, which does not solve the problem:
https://github.com/NativeScript/android-runtime/issues/1178

Start with the Feedback.show entry point in node_modules/nativescript-feedback/feedback.js at lines 15-17 and compare the failure with NativeScript/android-runtime issue 1178. Reproduce the call from the provided FeedbackService example in a new NativeScript project; done means invoking show no longer crashes with the final-field error.

Written by the indexing model from the issue text.