Correct battery-status "status" event name

src/plugins/batterystatus.ts

@@ -37,7 +37,7 @@ export class BatteryStatus {
    */
   @Cordova({
     eventObservable: true,
-    event: 'batterylevel'
+    event: 'batterystatus'
   })
   static onChange () : Observable<StatusObject> {return}
 
@@ -73,4 +73,4 @@ export interface StatusObject {
    * A boolean that indicates whether the device is plugged in
    */
   isPlugged : boolean
-}
+}