Add stream$Writable as a mixin to stream$Duplex
Add stream$Writable as a mixin to stream$Duplex

Summary:
Fixes #1850.

Signed-off-by: Joe Grund joe.grund@intel.com
Closes https://github.com/facebook/flow/pull/2529

Reviewed By: samwgoldman

Differential Revision: D4226792

Pulled By: gabelevi

fbshipit-source-id: 61fc93e144db9df0302023e0a612bef8d1d76733

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