Switch from system volume to media volume (#600)

- switch volume return from system volume to the music volume

Author: electrostat

mapbox/libandroid-telemetry/src/main/java/com/mapbox/services/android/telemetry/utils/TelemetryUtils.java

@@ -199,8 +199,8 @@ public static int getScreenBrightness(Context context) {
    */
   public static int getVolumeLevel(Context context) {
     AudioManager audioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
-    return (int) Math.floor(100.0 * audioManager.getStreamVolume(AudioManager.STREAM_SYSTEM)
-        / audioManager.getStreamMaxVolume(AudioManager.STREAM_SYSTEM));
+    return (int) Math.floor(100.0 * audioManager.getStreamVolume(AudioManager.STREAM_MUSIC)
+        / audioManager.getStreamMaxVolume(AudioManager.STREAM_MUSIC));
   }
 
   /**