Update link to example audio file, close raspberrypi#738

Author: bennuttall

usage/audio/README.md

@@ -1,6 +1,6 @@
 # Playing audio on the Raspberry Pi
 
-To play an MP3 file, navigate to the location of the .mp3 file in the terminal using `cd` and then type the following command: 
+To play an MP3 file, navigate to the location of the `.mp3` file in the terminal using `cd` and then type the following command: 
 
 ```bash
 omxplayer example.mp3
@@ -11,7 +11,7 @@ This will play the audio file `example.mp3` through either your monitor's built-
 If you need an example file you can download one from here using the following command:
 
 ```bash
-wget https://goo.gl/XJuOUW -O example.mp3 --no-check-certificate
+wget http://rpf.io/lamp3 -O example.mp3 --no-check-certificate
 ```
 
 If you cannot hear anything, make sure your headphones or speakers are connected correctly. Note that omxplayer doesn't use ALSA and so ignores the [audio configuration](../../configuration/audio-config.md) set by `raspi-config` or `amixer`.