Bump libnemesis to pick up test fixes.

This adds a bunch of team related tests, and ensures that the newly
added withdrawn_student doesn't cause any test failures.

Change-Id: I58ab16af36700ee5a74ab3f88aaa9f9440e32105
Bump libnemesis for can_withdraw(user) helper.

This determines if a user can withdraw another user.

Change-Id: I7850bd7f8ee05b4887f473d3b503d7858cbe15ac