fix build
fix build

Summary: fix typo

jenkins and oss build (e.g. travis) failing.

Reviewed By: @pavlo-fb

Differential Revision: D2499462

sonnyhu/folly,brunomorishita/folly,floxard/folly,rklabs/folly,floxard/folly,Hincoin/folly,sonnyhu/folly,Hincoin/folly,facebook/folly,Hincoin/folly,sonnyhu/folly,mqeizi/folly,facebook/folly,juniway/folly,Orvid/folly,facebook/folly,alexst07/folly,Orvid/folly,brunomorishita/folly,juniway/folly,mqeizi/folly,brunomorishita/folly,alexst07/folly,mqeizi/folly,facebook/folly,gaoyingie/folly,PPC64/folly,Hincoin/folly,charsyam/folly,Orvid/folly,rklabs/folly,juniway/folly,gaoyingie/folly,alexst07/folly,mqeizi/folly,rklabs/folly,sonnyhu/folly,floxard/folly,alexst07/folly,rklabs/folly,brunomorishita/folly,charsyam/folly,juniway/folly,charsyam/folly,PPC64/folly,floxard/folly,gaoyingie/folly,sonnyhu/folly,floxard/folly,Orvid/folly,Hincoin/folly,juniway/folly,gaoyingie/folly,mqeizi/folly,alexst07/folly,rklabs/folly,charsyam/folly,facebook/folly,gaoyingie/folly,brunomorishita/folly,PPC64/folly,PPC64/folly,Orvid/folly,PPC64/folly