build,travis: fix repo unshallowing

git merge-base does not work as I expected

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

.travis_do.sh

@@ -152,7 +152,8 @@ echo_blue "=== Travis ENV"
 env
 echo_blue "=== Travis ENV"
 
-until git merge-base ${TRAVIS_COMMIT_RANGE/.../ } > /dev/null; do
+until [ "$(git rev-list ${TRAVIS_COMMIT_RANGE/.../..} | tail -n1)" != "a22de9b74cf9579d1ce7e6cf1845b4afa4277b00" ]; do
+	# if clone depth is too small, git rev-list / diff return incorrect results
 	echo_blue "Fetching 50 commits more"
 	git fetch origin --deepen=50
 done