Usernames should be prevalidated with GitHub before submission completion

[QuincyLarson]

I accidentally typed "@Bouncey" into the "collaborators" field and it ended up showing me a broken image.

I think we can strip off leading @ signs in the event that people accidentally type these like I did.

[Bouncey]

We should add a test for this in `team.test.js`

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On Sat, 3 Nov 2018, 14:16 Kristofer Koishigawa ***@***.*** wrote: Reopened #22 <#22>. — You are receiving this because you modified the open/close state. Reply to this email directly, view it on GitHub <#22 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ARtk5skk7tNx6QK9adPSGHL_SxEEHmE2ks5uraUjgaJpZM4YMoOD> .