message: use the right branch
diff: #!/bin/sh
  +BLOCKSTACK_BRANCH="rc-0.14.2"
  +
  # needed on CircleCI's VMs
  pip install --upgrade pip
  pip install --upgrade six
  @@ -8,8 +10,11 @@ pip install --upgrade cryptography
  # install Blockstack and integration tests
  git clone https://github.com/blockstack/blockstack-core /tmp/blockstack-core
  +cd /tmp/blockstack-core && git checkout "$BLOCKSTACK_BRANCH"
  +
  cd /tmp/blockstack-core && ./setup.py build && ./setup.py install
  cd /tmp/blockstack-core/integration_tests && ./setup.py build && ./setup.py install
  +
  npm install -g babel
  npm install -g browserify
  