build,travis: accept commits with '_'

Signed-off-by: Etienne Champetier <champetier.etienne@gmail.com>

.travis_do.sh

@@ -158,7 +158,7 @@ test_commits() {
 		fi
 
 		subject="$(git show -s --format=%s $commit)"
-		if echo "$subject" | grep -q -e '^[0-9A-Za-z,/-]\+: ' -e '^Revert '; then
+		if echo "$subject" | grep -q -e '^[0-9A-Za-z,/_-]\+: ' -e '^Revert '; then
 			echo_green "Commit subject line seems ok ($subject)"
 		else
 			echo_red "Commit subject line MUST start with '<package name>: ' ($subject)"