Corrected MetaRunner due to changes in GitVersion

@robdmoore can you review the following?  If you are ok with them, hopefully they can get merged in.

Found a couple issues...

* When a checkout directory is not specified, the workingDir variable has a trailing \ which causes an issue when passing arguments into the GitVersion.exe
* If no password is specified in TeamCity configuration, the .Replace fails, therefore we should only do it if there is a password provided
* A new modification to the UpdateAssemblyInfo overload means that you need to specify the additional parameter, otherwise GitVersion fails to parse the arguments correctly