Migration: please emit ES6 output

[jrieken]

We have identified this extension as emitting ES5-JavaScript code and extending API-types, like vscode.Disposable or vscode.CompletionItem. VS Code itself has changed to emit ES6 JavaScript code and too enable functions extending from classes we have added a utility in our code. Given the small number of es5-emitting extensions that also extend API-types we ask for your help, which is emitting ES6 instead of ES5.

Thanks and #HappyCoding!