rolling has 36 now that it is artful (#3991)

diff --git a/Jenkinsfile b/Jenkinsfile
index a969f8a..0719907 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -71,7 +71,7 @@
     [
         label: 'docker',
         imageName: 'pyca/cryptography-runner-ubuntu-rolling',
-        toxenvs: ['py27', 'py35', 'randomorder'],
+        toxenvs: ['py27', 'py36', 'randomorder'],
     ],
     [
         label: 'docker',