Require urllib3 tests to pass; fixes #712 (#716)

diff --git a/.travis.yml b/.travis.yml
index c76dc45..9dc734c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -88,9 +88,6 @@
   - env: TOXENV=py35-cryptographyMaster
   - env: TOXENV=py36-cryptographyMaster
   - env: TOXENV=pypy-cryptographyMaster
-  # TODO: undo this once upstream fixes their tests
-  - python: "3.5"
-    env: TOXENV=py35-urllib3Master
 
 
 install: