fix HHWheelTimer comment typo
fix HHWheelTimer comment typo

Summary: Noticed this while reading the code.

Reviewed By: yfeldblum

Differential Revision: D3648565

fbshipit-source-id: c00940e5ce91fbc7e5cc6c42e35c5deee3e0bf65

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