Fixing typo in Readme
Fixing typo in Readme

Summary: Closes https://github.com/facebook/folly/pull/403

Reviewed By: yfeldblum

Differential Revision: D3320043

Pulled By: elliottneilclark

fbshipit-source-id: 5d21421216180fb601015a40a3de79e3dd2a162e

Orvid/folly,rklabs/folly,Orvid/folly,facebook/folly,brunomorishita/folly,facebook/folly,floxard/folly,floxard/folly,mqeizi/folly,floxard/folly,Orvid/folly,mqeizi/folly,charsyam/folly,mqeizi/folly,rklabs/folly,charsyam/folly,rklabs/folly,charsyam/folly,brunomorishita/folly,floxard/folly,mqeizi/folly,brunomorishita/folly,Orvid/folly,facebook/folly,floxard/folly,facebook/folly,brunomorishita/folly,rklabs/folly,Orvid/folly,rklabs/folly,mqeizi/folly,charsyam/folly,brunomorishita/folly,facebook/folly