fix race in incremental_non_flow_move test
fix race in incremental_non_flow_move test

Summary:
`incremental_non_flow_move` has been flaky on our internal Mac CI recently, failing because after the `mv tmp/foo.js .`, the `foo` module is still unknown. this suggests that Flow hasn't seen the file move yet, which is indeed a possible race.

this adds a 1s sleep to give it time.

a more ideal fix would be a command that waits for dfind to see a change, like `flow file-watcher-wait --timeout 1000 foo.js`, but does not trigger a recheck like `force-recheck` does. that is left for future work.

Reviewed By: panagosg7

Differential Revision: D27399309

fbshipit-source-id: b6fc58ffb88e546c83680bae55c3fa5b6854e634

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