Upgraded pypy to latest version

.travis.yml

@@ -27,13 +27,13 @@ matrix:
     env: TOX_ENV=py36-gce
   - python: 3.6
     env: TOX_ENV=py36-openstack
-  - python: pypy-5.3.1
+  - python: pypy-6.0
     env: TOX_ENV=pypy-aws
-  - python: pypy-5.3.1
+  - python: pypy-6.0
     env: TOX_ENV=pypy-azure
-  - python: pypy-5.3.1
+  - python: pypy-6.0
     env: TOX_ENV=pypy-gce
-  - python: pypy-5.3.1
+  - python: pypy-6.0
     env: TOX_ENV=pypy-openstack
 env:
   global: