docs: gitter isn't active

CONTRIBUTING.md

@@ -51,7 +51,7 @@ It's very important that your pull requests include all of the above in order fo
 
 ## Writing Tests
 
-Tests are written using [mocha](https://mochajs.org/), [chai](http://chaijs.com/) and [sinon](http://sinonjs.org/). If you are having issues making a test pass, ask for help in the SerialPort [gitter](https://gitter.im/serialport/node-serialport) room or on your PR. Tests can be the hardest part to write when contributing code, so don't be discouraged.
+Tests are written using [mocha](https://mochajs.org/), [chai](http://chaijs.com/) and [sinon](http://sinonjs.org/). If you are having issues making a test pass, ask for help in the SerialPort [discussions list](https://github.com/serialport/node-serialport/discussions) or on your PR. Tests can be the hardest part to write when contributing code, so don't be discouraged.
 
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