Bump GuiUnit.

New commits in mono/guiunit:

* mono/guiunit@40ed270 Print the full test name when showing labels. (dotnet#19)
* mono/guiunit@b05141d Print errors at the end. (dotnet#20)
* mono/guiunit@29faffa Merge pull request dotnet#18 from mono/update-gitignore
* mono/guiunit@22c0fdf Just ignore obj directories in general

Diff: https://github.com/mono/guiunit/compare/9affe4813987b009022ab7b10e55f81f4a37344c..40ed270ba75448ebadf3b995e73971cae4d47cba