refractor Observable imports

src/plugins/dbmeter.ts

@@ -1,5 +1,5 @@
 import {Plugin, Cordova} from './plugin';
-import {Observable} from 'rxjs/Observable';
+import {Observable} from 'rxjs/Rx';
 /**
  * @name DB Meter
  * @description This plugin defines a global DBMeter object, which permits to get the decibel values from the microphone.
@@ -68,4 +68,4 @@ export class DBMeter {
   @Cordova()
   static delete(): Promise<any> {return; }
 
-}
+}