Upgrade pip when building mac distribution

scripts/setup-osx.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 wget "https://www.python.org/ftp/python/${PYTHON}/python-${PYTHON}-macosx10.6.pkg"
 sudo installer -pkg python-${PYTHON}-macosx10.6.pkg -target /
-sudo python3 -m ensurepip
+sudo python3 -m ensurepip --upgrade
 # A manual check that the correct version of Python is running.
 python3 --version
 pip3 install -r requirements.txt