Update default regex message to match regex.

lib/gitlab/regex.rb

@@ -67,8 +67,7 @@ module Gitlab
 
     def default_regex_message
       "can contain only letters, digits, '_', '-' and '.'. " \
-      "It must start with letter, digit or '_', optionally preceeded by '.'. " \
-      "It must not end in '.git'."
+      "Cannot start with '-' or end in '.git'" \
     end
 
     def default_regex