python2 and clarified coverage

bootstrap/dev/venv.sh

@@ -1,6 +1,8 @@
 #!/bin/sh -xe
 # Developer virtualenv setup for Let's Encrypt client
 
+export VENV_ARGS="--python python2"
+
 ./bootstrap/dev/_venv_common.sh \
   -r requirements.txt \
   -e acme[testing] \

docs/contributing.rst

@@ -7,9 +7,9 @@ Contributing
 Hacking
 =======
 
-The code base, including your pull requests, **must** have 100% unit
+All changes in your pull request **must** have 100% unit test coverage, pass
-test coverage, pass our `integration`_ tests **and** be compliant with
+our `integration`_ tests, **and** be compliant with the
-the :ref:`coding style <coding-style>`.
+:ref:`coding style <coding-style>`.
 
 
 Bootstrap