email: Change stray SMTP_SERVER to server

This fixes the error below that occurred upon sending a message by SMTP.

NameError: global name 'SMTP_SERVER' is not defined.

Signed-off-by: George Saunders <georgesaunders@gmail.com>
Merge remote-tracking branch 'alienacorn/master'

* alienacorn/master:
  email: Change stray SMTP_SERVER to server

Signed-off-by: W. Trevor King <wking@tremily.us>