circleci: Install virtualenv

sschuberth · sschuberth · commit f32249ea8d77 · 2017-03-01T13:20:45.000+01:00
The default machine step calls virtualenv, which is not installed. Doh!
diff --git a/circle.yml b/circle.yml
@@ -1,6 +1,7 @@
 machine:
   pre:
     - python --version
+    - sudo -H pip install --upgrade virtualenv
     - brew install pyenv
     - echo 'eval "$(pyenv init -)"' >> ~/.bash_profile
     - source ~/.bash_profile
