Fix broken downloads badge in readme

Also changed the badge to show downloads per month instead of total

Author: m-lundberg

README.md

@@ -4,7 +4,7 @@
 [![PyPI](https://img.shields.io/pypi/v/simple-pid.svg)](https://pypi.org/project/simple-pid/)
 [![Read the Docs](https://img.shields.io/readthedocs/simple-pid.svg)](https://simple-pid.readthedocs.io/)
 [![License](https://img.shields.io/github/license/m-lundberg/simple-pid.svg)](https://github.com/m-lundberg/simple-pid/blob/master/LICENSE.md)
-[![Downloads](https://pepy.tech/badge/simple-pid)](https://pepy.tech/project/simple-pid)
+[![Downloads](https://static.pepy.tech/badge/simple-pid/month)](https://pepy.tech/project/simple-pid)
 [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
 
 A simple and easy to use PID controller in Python. If you want a PID controller without external dependencies that just works, this is for you! The PID was designed to be robust with help from [Brett Beauregards guide](http://brettbeauregard.com/blog/2011/04/improving-the-beginners-pid-introduction/).