Remove GitHub Action badge from README.rst

It was broken because of the breaking change on their side. Besides I
think it's broken by design as it always points to a hardcoded branch
and doesn't reflect a correct state of affairs.

README.rst

@@ -4,9 +4,6 @@ Picobox
 .. image:: https://img.shields.io/pypi/v/picobox.svg
    :target: https://pypi.python.org/pypi/picobox
 
-.. image:: https://img.shields.io/github/workflow/status/ikalnytskyi/picobox/ci/master
-   :target: https://github.com/ikalnytskyi/picobox
-
 .. image:: https://img.shields.io/badge/Say%20Thanks-!-1EAEDB.svg
    :target: https://saythanks.io/to/ikalnytskyi