Docs: Sets default code block language in issue template to "ts" (eslint#421)

Author: mariusschulz

Diff for: .github/ISSUE_TEMPLATE.md

@@ -6,8 +6,8 @@
 
 **What code were you trying to parse?**
 
-```
-<!-- put your code here -->
+```ts
+// Put your code here
 ```
 
 **What did you expect to happen?**