docs: remove Gitter from issue templates (#186)

Author: ersachin3112

.github/ISSUE_TEMPLATE/BUG.md

@@ -11,7 +11,7 @@ about: Something went awry and you'd like to tell us about it.
   while making animal noises.
 
   👉🏽 Need support, advice, or help? Don't open an issue!
-  Head to StackOverflow or https://gitter.im/webpack/webpack.
+  Head to StackOverflow.
 -->
 
 - Operating System:

.github/ISSUE_TEMPLATE/DOCS.md

@@ -11,7 +11,7 @@ about: Are the docs lacking or missing something? Do they need some new 🔥 hot
   while making animal noises.
 
   👉🏽 Need support, advice, or help? Don't open an issue!
-  Head to StackOverflow or https://gitter.im/webpack/webpack.
+  Head to StackOverflow.
 -->
 
 Documentation Is:

.github/ISSUE_TEMPLATE/FEATURE.md

@@ -11,7 +11,7 @@ about: Suggest an idea for this project
   while making animal noises.
 
   👉🏽 Need support, advice, or help? Don't open an issue!
-  Head to StackOverflow or https://gitter.im/webpack/webpack.
+  Head to StackOverflow.
 -->
 
 - Operating System:

.github/ISSUE_TEMPLATE/MODIFICATION.md

@@ -11,7 +11,7 @@ about: Would you like something work differently? Have an alternative approach?
   while making animal noises.
 
   👉🏽 Need support, advice, or help? Don't open an issue!
-  Head to StackOverflow or https://gitter.im/webpack/webpack.
+  Head to StackOverflow.
 -->
 
 - Operating System:

.github/ISSUE_TEMPLATE/SUPPORT.md

@@ -4,5 +4,4 @@ about: 👉🏽 Need support, help, or advice? Don't open an issue! Head to Stac
 ---
 
 Hey there! If you need support, help, or advice then this is not the place to ask.
-Please visit [StackOverflow](https://stackoverflow.com/questions/tagged/webpack)
-or [the Webpack Gitter](https://gitter.im/webpack/webpack) instead.
+Please visit [StackOverflow](https://stackoverflow.com/questions/tagged/webpack).