Remove defunct Gitter badge from README

Author: xtqqczze

README.md

@@ -3,7 +3,6 @@
 <img src="logo.png" width="180">
 
 [![Build Status](https://dev.azure.com/powershell/psscriptanalyzer/_apis/build/status/psscriptanalyzer-ci?branchName=master)](https://dev.azure.com/powershell/psscriptanalyzer/_build/latest?definitionId=80&branchName=master)
-[![Join the chat at https://gitter.im/PowerShell/PSScriptAnalyzer](https://badges.gitter.im/PowerShell/PSScriptAnalyzer.svg)](https://gitter.im/PowerShell/PSScriptAnalyzer?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 
 ## Table of Contents