feat(Transition): allow custom animations

[jongsue]

Fixes #3323.

[codecov-io]

Codecov Report

Merging #3438 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #3438   +/-   ##
=======================================
  Coverage   99.92%   99.92%           
=======================================
  Files         172      172           
  Lines        2819     2819           
=======================================
  Hits         2817     2817           
  Misses          2        2

Impacted Files	Coverage Δ
src/modules/Transition/Transition.js	100% <100%> (ø)	⬆️
src/modules/Transition/TransitionGroup.js	100% <100%> (ø)	⬆️

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[layershifter]

Added small styling changes, LGTM! Good job 👍

[jongsue]

Thank you for review @layershifter 👍

[levithomason]

Released in [email protected].