[hack] files in optional in watchman subscription response
[hack] files in optional in watchman subscription response

Summary: Files is optional in watchman subscription response. See also docs in code.

Reviewed By: oulgen

Differential Revision: D4059439

fbshipit-source-id: 77e3c7640acb6e7f324954a7a17364344dec95aa

AprilArcus/flow,jamesgpearce/flow,samwgoldman/flow,fletcherw/flow,popham/flow,jamesgpearce/flow,samwgoldman/flow,ForbesLindesay/flow,ForbesLindesay/flow,fletcherw/flow,gabro/flow,ylu1317/flow,TiddoLangerak/flow,jgrund/flow,JonathanUsername/flow,JonathanUsername/flow,jgrund/flow,mroch/flow,TiddoLangerak/flow,popham/flow,popham/flow,samwgoldman/flow,gabelevi/flow,jamesgpearce/flow,nmote/flow,JonathanUsername/flow,gabro/flow,mroch/flow,MichaelDeBoey/flow,jgrund/flow,JonathanUsername/flow,ylu1317/flow,gabelevi/flow,fletcherw/flow,mroch/flow,jamesgpearce/flow,gabelevi/flow,facebook/flow,gabelevi/flow,jamesgpearce/flow,AprilArcus/flow,gabro/flow,claudiopro/flow,mroch/flow,TiddoLangerak/flow,mroch/flow,nmote/flow,ylu1317/flow,nmote/flow,jgrund/flow,nmote/flow,ForbesLindesay/flow,JonathanUsername/flow,ylu1317/flow,popham/flow,popham/flow,MichaelDeBoey/flow,facebook/flow,gabro/flow,facebook/flow,gabelevi/flow,facebook/flow,claudiopro/flow,claudiopro/flow,TiddoLangerak/flow,facebook/flow,AprilArcus/flow,nmote/flow,nmote/flow,ForbesLindesay/flow,mroch/flow,samwgoldman/flow,claudiopro/flow,MichaelDeBoey/flow,gabelevi/flow,ForbesLindesay/flow,claudiopro/flow,jgrund/flow,popham/flow,fletcherw/flow,jamesgpearce/flow,ForbesLindesay/flow,JonathanUsername/flow,AgentME/flow,AgentME/flow,popham/flow,AprilArcus/flow,AgentME/flow,AgentME/flow,TiddoLangerak/flow,fletcherw/flow,ylu1317/flow,samwgoldman/flow,AgentME/flow,fletcherw/flow,AprilArcus/flow,jamesgpearce/flow,facebook/flow,gabelevi/flow,gabro/flow,AprilArcus/flow,samwgoldman/flow,nmote/flow,jgrund/flow,facebook/flow,JonathanUsername/flow,mroch/flow,MichaelDeBoey/flow,MichaelDeBoey/flow,gabro/flow,samwgoldman/flow