README: fix link for CI status badge

The default branch was renamed from master to main, but the badge was still
linking to the status for the master branch.

Remove the branch-name so that the badge always refers to the "default"
branch

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

README.md

@@ -1,6 +1,6 @@
 # Docker SDK for Python
 
-[![Build Status](https://github.com/docker/docker-py/actions/workflows/ci.yml/badge.svg?branch=master)](https://github.com/docker/docker-py/actions/workflows/ci.yml/)
+[![Build Status](https://github.com/docker/docker-py/actions/workflows/ci.yml/badge.svg)](https://github.com/docker/docker-py/actions/workflows/ci.yml)
 
 A Python library for the Docker Engine API. It lets you do anything the `docker` command does, but from within Python apps – run containers, manage containers, manage Swarms, etc.