Use getExternalFilesDir() instead of getExternalStorageDirectory

[diegopap]

Writing to this path requires the WRITE_EXTERNAL_STORAGE permission.

Starting in KITKAT, if your application only needs to store internal data, consider using getExternalFilesDir(String), getExternalCacheDir(), or getExternalMediaDirs(), which require no permissions to read or write.

Source:
http://developer.android.com/intl/es/reference/android/os/Environment.html#getExternalStorageDirectory()