Improve highlighting of code samples

SC1039.md

@@ -5,9 +5,9 @@
 ```sh
 for f in *.png
 do
-  cat << EOF
+  cat << HTML
      <img src="$f" /><br/>
-  EOF
+  HTML
 done > index.html
 ```
 
@@ -16,11 +16,12 @@ done > index.html
 ```sh
 for f in *.png
 do
-  cat << EOF
+  cat << HTML
      <img src="$f" /><br/>
-EOF
+HTML
 done > index.html
 ```
+
 ### Rationale:
 
 The here document delimiter will not be recognized if it is indented.