Also fix a typo in ValidateEmail function which didn't support
email addresses with '-' in them, e.g., infra-dev@chromium.org.

R=ehmaldonado

Bug: 875089
Change-Id: I2d73c1473527c9bf62e25e9f88250196b783fcb0
Reviewed-on: https://chromium-review.googlesource.com/c/1242849
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>