Add a workaround for Python 3.7 build failure.
It looks like the build fails on travis because of old setuptools.
@@ -9,6 +9,7 @@ deps =
lockfile
libvirt-python==4.0.0
py2.7: paramiko
+ py3.7: setuptools==41.0.1
commands = cp libcloud/test/secrets.py-dist libcloud/test/secrets.py
python setup.py test
basepython =
