update bug report issue template (cosmos#1693)

Author: colin-axner

.github/ISSUE_TEMPLATE/bug-report.md

@@ -20,6 +20,10 @@ through the appropriate channels won't receive any bounty.
 
 <!-- Concisely describe the issue -->
 
+## Expected Behaviour
+
+<!-- What is the expected behaviour? -->
+
 ## Version
 
 <!-- git commit hash or release version -->