ttf-google-fonts-git: add 'cantarell-fonts' as a dependency and remove
Cantarell from this package

This change is needed because the cantarell-fonts package (a part of
GNOME) ships a better/improved version of the original Cantarell font,
which Google ships as part of the Google Fonts project.
Merge pull request #3 from jrstjohn/google-fonts-cantarell-depends

Add 'cantarell-fonts' as a dependency of 'ttf-google-fonts-git'