only take the last commit to diff (#1920)
only take the last commit to diff (#1920)

Only compare to parent, not grand parent. Not sure why it's previously been ~2.
You can try `git diff HEAD~2 --name-only` and `git diff HEAD~1 --name-only` in master to see that the first one actually returns names for two last merged libdefs instead of one.

Noticed this behaviour here: https://github.com/flowtype/flow-typed/pull/1919 See the travis output where unrelated libdefs fails: https://travis-ci.org/flowtype/flow-typed/jobs/350025576
orlandoc01/flow-typed,mwalkerwells/flow-typed,splodingsocks/FlowTyped,mwalkerwells/flow-typed,orlandoc01/flow-typed,splodingsocks/FlowTyped,doberkofler/flow-typed,flowtype/flow-typed,flowtype/flow-typed,doberkofler/flow-typed