Fix pipeline (#68)

* Upgrade pip

* Don't build rust in cryptography in py36

* Force install cryptography<3.4 on py36

* Update .travis.yml

* Update tox.ini

* Update .travis.yml

* Update tox.ini

* Update tox.ini

Author: awarecan

tox.ini

@@ -24,4 +24,7 @@ commands =
     pip install -U pip
     py.test --basetemp={envtmpdir}
 
-
+[testenv:py36]
+deps =
+    cryptography>=3,<3.4
+    -r{toxinidir}/requirements_dev.txt