v1.2.4

- Fixed AttributeError when using --use-afdko option (#313)
- Cleaned up workflow for Monotype feature files; these are now embedded
  into the master UFOs so that they are fully self-contained (#290, #292)
- Fixed "'dict_keys' object does not support indexing" in python 3
- Bumped minimum requirements:
    * fonttools 3.11.0
    * glyphsLib 1.7.2
    * ufo2ft 0.5.0
    * MutatorMath 2.0.4