Try to fix travis issue upgrading setuptools.

Makefile

@@ -152,7 +152,7 @@ develop:
 # First install a newer pip so that it can use the wheel cache
 # (only needed until travis upgrades pip to 7.x; note that the 3.5
 # environment uses pip 7.1 by default)
-	${PIP} install -U pip
+	${PIP} install -U pip setuptools
 # Then start installing our deps so they can be cached. Note that use of --build-options / --global-options / --install-options
 # disables the cache.
 # We need wheel>=0.26 on Python 3.5. See previous revisions.