requirements: un-pin skia-pathops for now
requirements: un-pin skia-pathops for now

I messed up skia-pathops setup.py's python_requires, so attempting to install v0.2.1 with python3.6 fails.

https://github.com/fonttools/skia-pathops/commit/c1c8b4630cde790551a3d11486e8e016ac18defa

Keep it un-pinned until v0.2.2 is released.

googlefonts/fontmake,googlefonts/fontmake,googlei18n/fontmake,googlei18n/fontmake