Remove Cabot (unmaintained) (#527)

Cabot last commit is dated from Jan 2021.

Furthermore its code base is not compatible with Python 3.x and requires Python 2.7. Python 2.7 is unmaintained and does no receive security support since 01 Jan 2020

README.md

@@ -471,7 +471,6 @@ _Related: [Metrics & Metric Collection](#metrics--metric-collection)_
 - [Alerta](https://alerta.io/) - Distributed, scalable and flexible monitoring system. ([Source Code](https://github.com/alerta/alerta)) `Apache-2.0` `Python`
 - [Bloonix](https://bloonix-monitoring.org/) - Bloonix is a monitoring solution that helps businesses to ensure high availability and performance. ([Source Code](https://github.com/bloonix)) `GPL-3.0` `Perl`
 - [Bosun](https://bosun.org/) - Monitoring and alerting system by Stack Exchange. ([Source Code](https://github.com/bosun-monitor/bosun)) `MIT` `Go`
-- [Cabot](https://cabotapp.com/) - Monitoring and alerts, similar to PagerDuty. ([Source Code](https://github.com/arachnys/cabot)) `MIT` `Python`
 - [Cacti](https://www.cacti.net) - Web-based network monitoring and graphing tool. ([Source Code](https://github.com/Cacti/cacti)) `GPL-2.0` `PHP`
 - [cadvisor](https://github.com/google/cadvisor) - Analyzes resource usage and performance characteristics of running containers. ([Source Code](https://github.com/google/cadvisor)) `Apache-2.0` `Go`
 - [checkmk](https://checkmk.com/) - Comprehensive solution for monitoring of applications, servers, and networks. ([Source Code](https://github.com/Checkmk/checkmk)) `GPL-2.0` `Python/PHP`