Fix Makefile.am
Fix Makefile.am

Summary: Fix line continuation.

Reviewed By: yuxuanchen1997

Differential Revision: D18248088

fbshipit-source-id: 35cfe43fd7350ca14c140065bbf19d207503c479

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