siultaneous tracking requests fail, expecting outdated/changed hash

I should have screen shotted the error, my apologies for not doing so.

Repro:
1. open multiple keybase.io/$userName tabs
2. attempt to track at least 2 different users at the same time (quickly switch browser tabs and send tracking request)
3. only one request will succeed - all others will output an error showing the key they were expecting and a different key to the one they recieved

Expected behaviour: all track requests should have succeeded given the correct passphrase

Actual behaviour: only one track request succeeded

Keep up the great work!

Reproduce by opening multiple keybase.io/$userName tabs and sending tracking requests for at least two users in quick succession. Compare the expected and received keys in the error; done means all tracking requests succeed with the correct passphrase.

Written by the indexing model from the issue text.