LinearTimingSource: return Promise (#6)

amendment to #6

src/Playback/TimingSources/LinearTimingSource.ts

@@ -28,14 +28,14 @@ export class LinearTimingSource extends AbstractTimingSource {
         return timestamp;
     }
 
-    public start(): void {
+    public start(): Promise<void> {
         console.log("Start linear timing source");
-        this.audioContext.resume();
+        return this.audioContext.resume();
     }
 
-    public pause(): void {
+    public pause(): Promise<void> {
         console.log("Pause linear timing source");
-        this.audioContext.suspend();
+        return this.audioContext.suspend();
     }
 
     public reset(): void {