lint: Fix gitlint checking commits in master but not in the branch.

This was causing a bunch of spurious failures.

Workaround for travis-ci/travis-ci#4596 ;
TRAVIS_COMMIT_RANGE is actually just totally wrong for this purpose.

tools/commit-message-lint

@@ -5,10 +5,11 @@
 
 # The rules can be found in /.gitlint
 
-if [ $TRAVIS ]; then
-    range=$TRAVIS_COMMIT_RANGE
+if [ "$TRAVIS" ]; then
+    # Work around https://github.com/travis-ci/travis-ci/issues/4596
+    range="${TRAVIS_COMMIT_RANGE/.../..}"
 else
-    range="upstream/master...HEAD"
+    range="upstream/master..HEAD"
 fi
 
 gitlint --commits $range