Typo fix

Fixes a typo in one of the validation messages, and centers the "dealer
application" heading.
``<center>`` is no longer a valid HTML tag and has been deprecated.  There are probably places in Uber where we have it left over from like 7 years ago or something, but in general you should avoid it since it's not guaranteed to work.  (In practice I'm guessing browsers will still support it for a long time, so no big deal.)