Removes need to use babel-register (#4865)

* Removes need to use babel-register

- Adds watch to watch changes when running the test to regenerate
- Tests are now pure node 8

* Adds timing to helper.js

* Update contribution guide

* Adds inline sourcemaps generation to restore coverage

* nits

src/Push/PushWorker.js

@@ -42,12 +42,6 @@ export class PushWorker {
     }
   }
 
-  unsubscribe(): void {
-    if (this.subscriber) {
-      this.subscriber.unsubscribe(this.channel);
-    }
-  }
-
   run({ body, query, pushStatus, applicationId, UTCOffset }: any): Promise<*> {
     const config = Config.get(applicationId);
     const auth = master(config);
@@ -59,8 +53,6 @@ export class PushWorker {
         return;
       }
       return this.sendToAdapter(body, results, pushStatus, config, UTCOffset);
-    }, err => {
-      throw err;
     });
   }