Fix code of conduct link.
Fix code of conduct link.

Summary: Thanks cmarkle for noticing in https://github.com/facebookincubator/fizz/pull/5

Reviewed By: dark

Differential Revision: D9195501

fbshipit-source-id: bdbe1588cdcd353d60fcaab14a4fac8bd2256355

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift