Update ISSUE_TEMPLATE.md

ISSUE_TEMPLATE.md

 > If you'd like to request an icon, please provide the following information:
 > - icon name
 > - at least one use case
-> - screenshot of similar icon
+> - screenshots of similar icons
 >
-> Please create one issue for each icon request.
\ No newline at end of file
+> Please create one issue for each icon request.