remove dup filenames

Author: sagivo

README.md

@@ -41,7 +41,6 @@ and rename file correspond to sound type:
 ```
 incallmanager_busytone.mp3  
 incallmanager_ringback.mp3  
-incallmanager_ringback.mp3  
 ```
 
 on android, as long as your file extension supported by android, this module will load it.
@@ -77,7 +76,6 @@ if you want to use bundled ringtone/ringback/busytone sound instead of system so
 ```
 incallmanager_busytone.mp3
 incallmanager_ringback.mp3  
-incallmanager_ringback.mp3  
 ```
 
 on ios, we only support mp3 files currently.