quickSuggestions do not trigger when defining a new JSON key. Fixes microsoft/monaco-editor#2579

src/languageFeatures.ts

@@ -321,7 +321,7 @@ export class CompletionAdapter implements languages.CompletionItemProvider {
 	constructor(private _worker: WorkerAccessor) {}
 
 	public get triggerCharacters(): string[] {
-		return [' ', ':'];
+		return [' ', ':', '"'];
 	}
 
 	provideCompletionItems(