Upgrade pystache from 0.5.3 to 0.5.4 (#9929)
Upgrade pystache from 0.5.3 to 0.5.4 (#9929)

Bugfix: made test with filenames OS agnostic
https://github.com/defunkt/pystache/blob/master/HISTORY.md#history
benjyw/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,pantsbuild/pants,pantsbuild/pants,pantsbuild/pants,benjyw/pants,pantsbuild/pants,jsirois/pants,benjyw/pants,jsirois/pants,pantsbuild/pants,benjyw/pants,pantsbuild/pants,jsirois/pants,benjyw/pants