Fix for #232: GitHubVersion for pull requests are not working with dynamic repositories

This test is wrong. If we want GitVersion to produce lowercase it should be changed at:

https://github.com/Particular/GitVersion/blob/master/GitVersionCore/GitHubFlow/BuildNumberCalculator.cs#L36
https://github.com/Particular/GitVersion/blob/master/GitVersionCore/GitFlow/BranchFinders/DevelopBasedVersionFinderBase.cs#L26