Fix typo in BBR docstring
Fix typo in BBR docstring

Summary: on RTT => one RTT

Reviewed By: sharma95

Differential Revision: D17448689

fbshipit-source-id: d09b94ff5d45b36a8dcf62ae00af8b89adc3c303

facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst