docs: remove Gitter from issue templates (#187)

Author: ersachin3112

.github/ISSUE_TEMPLATE/SUPPORT.md

@@ -1,6 +1,6 @@
 ---
 name: 🆘 Support, Help, and Advice
-about: 👉🏽 Need support, help, or advice? Don't open an issue! Head to StackOverflow or https://gitter.im/webpack/webpack.
+about: 👉🏽 Need support, help, or advice? Don't open an issue! Head to StackOverflow.
 ---
 
 Hey there! If you need support, help, or advice then this is not the place to ask.