Add missing dependency for latest gsutil

.travis.yml

@@ -5,6 +5,7 @@ env:
   - PATH="${PATH}:${HOME}/gsutil"
 
 install:
+  - pip install pyopenssl
   - curl --silent --location https://storage.googleapis.com/pub/gsutil.tar.gz | tar xz -C $HOME
   - bin/setup-ci-secrets $encrypted_5ba036e89377_key $encrypted_5ba036e89377_iv