Make shared_ptr explicit (#466)
Make shared_ptr explicit (#466)

Summary:
Pull Request resolved: https://github.com/facebook/redex/pull/466

I heard that the old Travis GCC is unhappy with the emplace w/o `shared_ptr`.

Reviewed By: amnn

Differential Revision: D20613667

fbshipit-source-id: f13d452bf65725bffedf7145393c3ddf98bc5499

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex