Invalid Package - Sharepoint Framework Extensions

import { override } from '@microsoft/decorators';
import { Log } from '@microsoft/sp-core-library';
import {
BaseApplicationCustomizer, Placeholder
} from '@microsoft/sp-application-base';
import { escape } from '@microsoft/sp-lodash-subset';

import * as strings from 'appInsightsDemoSpFxExtensionStrings';

const LOG_SOURCE: string = 'AppInsightsDemoSpFxExtensionApplicationCustomizer';

/**
* If your command set uses the ClientSideComponentProperties JSON input,
* it will be deserialized into the BaseExtension.properties object.
* You can define an interface to describe it.
*/
export interface IAppInsightsDemoSpFxExtensionApplicationCustomizerProperties {
Header: string;
}

/** A Custom Action which can be run during execution of a Client Side Application */
export default class AppInsightsDemoSpFxExtensionApplicationCustomizer
extends BaseApplicationCustomizer<IAppInsightsDemoSpFxExtensionApplicationCustomizerProperties> {

// Header reference
private _headerPlaceholder: Placeholder;

@override
public onInit(): Promise<void> {
Log.info(LOG_SOURCE, `Initialized ${strings.Title}`);
return Promise.resolve<void>();
}

@override
public onRender(): void {
let html: string = '';
html+= `<script type="text/javascript">
"var appInsights=window.appInsights||function(config){
function i(config){t[config]=function(){var i=arguments;t.queue.push(function(){t[config].apply(t,i)})}}var t={config:config},u=document,e=window,o="script",s="AuthenticatedUserContext",h="start",c="stop",l="Track",a=l+"Event",v=l+"Page",y=u.createElement(o),r,f;y.src=config.url||"https://az416426.vo.msecnd.net/scripts/a/ai.0.js";u.getElementsByTagName(o)[0].parentNode.appendChild(y);try{t.cookie=u.cookie}catch(p){}for(t.queue=[],t.version="1.0",r=["Event","Exception","Metric","PageView","Trace","Dependency"];r.length;)i("track"+r.pop());return i("set"+s),i("clear"+s),i(h+a),i(c+a),i(h+v),i(c+v),i("flush"),config.disableExceptionTracking||(r="onerror",i("_"+r),f=e[r],e[r]=function(config,i,u,e,o){var s=f&&f(config,i,u,e,o);return s!==!0&&t["_"+r](config,i,u,e,o),s}),t
}({
instrumentationKey:"b4cf6d1c-5d38-48ce-ac4e-8a7802f2a1a0"
})
 
window.appInsights=appInsights;
appInsights.trackPageView();
</script>`;

console.log('CustomHeader.onRender()');

// Handling header place holder
if (!this._headerPlaceholder) {
this._headerPlaceholder = this.context.placeholders.tryAttach(
'PageHeader',
{
onDispose: this._onDispose
});

// The extension should not assume that the expected placeholder is available.
if (!this._headerPlaceholder) {
console.error('The expected placeholder was not found.');
return;
}

if (this.properties) {
let headerString: string = this.properties.Header;
if (!headerString) {
headerString = '(Header property was not defined.)';
}

if (this._headerPlaceholder.domElement) {
this._headerPlaceholder.domElement.innerHTML = html;
console.log('injected');
//alert('hello world');
}
}
}
}

private _onDispose(): void {
console.log('[CustomHeader._onDispose] Disposed custom header.');
}
}