Update Protobuild

This fixes some issues on the Mac platform, in particular the latest version of Xamarin Studio no longer seems to like having the Configuration variable in the OutputPath or IntermediateOutputPath properties.

The changes between the current version MonoGame will have and the new version can be found at: https://github.com/hach-que/Protobuild/compare/e4852cbb1f9c00f7eace1cf4f71f62c5c4657858...9ec55174994410bcc9b7e9e1c36f0b47757f0731