Fix git_commit_hashes hook so pre-release assemblies can build

Fix the git_commit_hashes hook, so the pre-release number is added to `AssemblyInformationalVersion`, not the `AssemblyVersion`.


:mag: @lukesmith 
Missed this before, should be `build_version_full`. Caps means constant in Ruby so I think this would be setting a const on the instance rather than being a local variable.