Replace infix Lwt.map with let%lwt
Replace infix Lwt.map with let%lwt

Summary: This is, in my opinion, more understandable, plus it makes the modifications to this file in the next diff a bit simpler.

Reviewed By: mroch

Differential Revision: D27577167

fbshipit-source-id: 0febaf9d22fa4f5a66898ed38b0a71f337d7159d

mroch/flow,facebook/flow,facebook/flow,mroch/flow,facebook/flow,mroch/flow,facebook/flow,mroch/flow,mroch/flow,facebook/flow,facebook/flow,mroch/flow,facebook/flow,mroch/flow