Fix PyPI version badge by switching from badge.fury.io to shields.io

The badge.fury.io service was showing stale cached version (0.1.0) despite PyPI having the correct version (0.1.1). Switched to shields.io which is more reliable and updates faster.

Author: jeremymanning

README.md

@@ -1,7 +1,7 @@
 # Clustrix
 
 [![Tests](https://github.com/ContextLab/clustrix/actions/workflows/tests.yml/badge.svg)](https://github.com/ContextLab/clustrix/actions/workflows/tests.yml)
-[![PyPI version](https://badge.fury.io/py/clustrix.svg)](https://badge.fury.io/py/clustrix)
+[![PyPI version](https://img.shields.io/pypi/v/clustrix.svg)](https://pypi.org/project/clustrix/)
 [![Documentation](https://readthedocs.org/projects/clustrix/badge/?version=latest)](https://clustrix.readthedocs.io/en/latest/?badge=latest)
 [![Python 3.8+](https://img.shields.io/badge/python-3.8+-blue.svg)](https://www.python.org/downloads/)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)