[try] fix typeatpos and ast using wrong version of flow
[try] fix typeatpos and ast using wrong version of flow

Summary:
the version selector calls `editor.setOption('flow', flowProxy)`. if we
hold onto a reference to `flowProxy` instead of calling
`editor.getOption('flow')`, then we don't use the correct version.

Reviewed By: calebmer

Differential Revision: D5409607

fbshipit-source-id: 44f7bb3195929bf90c784ca3ba0f2f23bccc3aa1

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