Update GettingStartedDeb.md

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Author: glennc

GettingStartedDeb.md

@@ -22,7 +22,8 @@ Mono is how .NET applications can run on platforms other than Windows. Mono is a
 To get these builds you need to run:
 
 ```
-echo "deb http://download.mono-project.com/repo/debian alpha main" | sudo tee /etc/apt/sources.list.d/mono-xamarin-alpha.list
+sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
+echo "deb http://download.mono-project.com/repo/debian wheezy main" | sudo tee /etc/apt/sources.list.d/mono-xamarin.list
 sudo apt-get update
 ```