fix(sms-retriever): update startWatching result type (#4309)

* Updating the types to match what we get

* Update index.ts

src/@awesome-cordova-plugins/plugins/sms-retriever/index.ts

@@ -41,7 +41,7 @@ export class SmsRetriever extends AwesomeCordovaNativePlugin {
    * @returns {Promise<string>} Returns a promise that resolves when retrives SMS text or TIMEOUT after 5 min.
    */
   @Cordova()
-  startWatching(): Promise<string> {
+  startWatching(): Promise<{ Message: string }> {
     return;
   }