readme: replace gitter link with discord

README.md

@@ -1,7 +1,7 @@
 # Web3.py
 
 [![Documentation Status](https://readthedocs.org/projects/web3py/badge/?version=latest)](https://web3py.readthedocs.io/en/latest/?badge=latest)
-[![Join the chat at https://gitter.im/ethereum/web3.py](https://badges.gitter.im/ethereum/web3.py.svg)](https://gitter.im/ethereum/web3.py?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+[![Discord](https://img.shields.io/discord/809793915578089484?color=blue&label=chat&logo=discord&logoColor=white)](https://discord.gg/GHryRvPB84)
 [![Build Status](https://circleci.com/gh/ethereum/web3.py.svg?style=shield)](https://circleci.com/gh/ethereum/web3.py)
 
 A Python library for interacting with Ethereum, inspired by [web3.js](https://github.com/ethereum/web3.js).