Improve aesthetics of commit hook rejection message

Summary: See PHI939. Ref T13216. Make the dragon's companion animal more clearly cow-like.

Test Plan:
Before:

\     \__/
 \____(Oo)
 (    (--)
 //__\\
//    \\

After:

*     \__/
 \____(Oo)
 (    (..)
 //___\\
//     \\

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13216

Differential Revision: https://secure.phabricator.com/D19775