Fixed muting issue on Windows 8

Hey,

I was having issues with the Mute/UnMute button not working. I am running Windows 8 with the latest version of Spotify.

Anyways I played around with the nircmdc command and noticed that it only worked if spotify.exe is capitalized in the muteappvolume command. Anyone else having this issue? I am not sure if it is OS specific. 

Cheers,
P