Fix CI badge target.
PEX
***
.. image:: https://github.com/pantsbuild/pex/workflows/CI/badge.svg?branch=master
- :target: https://travis-ci.org/pantsbuild/pex
+ :target: https://github.com/pantsbuild/pex/actions?query=branch%3Amaster+workflow%3ACI
.. image:: https://img.shields.io/pypi/l/pex.svg
:target: https://pypi.org/project/pex/
.. image:: https://img.shields.io/pypi/v/pex.svg
