Swap out link to StackOverflow, which fails verification (#1495)

Author: kevmoo

.github/ISSUE_TEMPLATE.md

@@ -4,9 +4,5 @@ In order to route, prioritize, and act on this, please include the entire output
 of either `dart --version` or `flutter --version`, depending on what
 you're using.
 
-Is it really an issue? For general questions consider starting with Stack
-Overflow:
-https://stackoverflow.com/questions/tagged/dart
-
-Also consider our Gitter channel for light-weight/quick discussions:
-https://gitter.im/dart-lang/build
+Is it really an issue? For general questions consider starting with community
+resources: https://dart.dev/community