dashboard: Don't highlight first heading row.
dashboard: Don't highlight first heading row.

The two heading rows were previously a little hard to pick out,
because they were alternately shaded like the commit rows.

R=adg
CC=golang-dev
http://codereview.appspot.com/5500074
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go