issue template: more general header

There might be other kind of output than the compilation output that
could be provided.

Author: smarter

.github/ISSUE_TEMPLATE/bug.md

@@ -13,10 +13,10 @@ assignees: ''
 println("hello, world")
 ```
 
-## Compilation output
+## Output
 
 ```scala
-// TODO add compilation output here
+// TODO add output here
 ```
 
 ## expectation

.github/ISSUE_TEMPLATE/crash.md

@@ -13,7 +13,7 @@ assignees: ''
 println("hello, world")
 ```
 
-## Crash output (click arrow to expand)
+## Output (click arrow to expand)
 <details>
 
 ```scala

.github/ISSUE_TEMPLATE/other-issue.md

@@ -13,10 +13,10 @@ assignees: ''
 println("hello, world")
 ```
 
-## Compilation output
+## Output
 
 ```scala
-// TODO add compilation output here
+// TODO add output here
 ```
 
 ## expectation