fix(smartstate): Fix StateAction trigger method to properly return Promise

ts/smartstate.classes.stateaction.ts

@@ -14,7 +14,7 @@ export class StateAction<TStateType, TActionPayloadType> {
     public actionDef: IActionDef<TStateType, TActionPayloadType>
   ) {}
 
-  public trigger(payload: TActionPayloadType) {
-    this.statePartRef.dispatchAction(this, payload);
+  public trigger(payload: TActionPayloadType): Promise<TStateType> {
+    return this.statePartRef.dispatchAction(this, payload);
   }
 }