[Gene] Fix type issue with dynamic object key typing.
[Gene] Fix type issue with dynamic object key typing.

See https://stackoverflow.com/questions/42090191/picks-k-type-with-dynamic-computed-keys/42131589#42131589

artsy/reaction,artsy/reaction-force,artsy/reaction,artsy/reaction-force,artsy/reaction,xtina-starr/reaction,xtina-starr/reaction,xtina-starr/reaction,xtina-starr/reaction