Update contributing/content-markup-reference.md

Co-authored-by: Ethan Palm <56270045+ethanpalm@users.noreply.github.com>

contributing/content-markup-reference.md

@@ -80,7 +80,7 @@ Within the command-line syntax, use all uppercase text to indicate placeholder t
 
 You can also add a header that includes the name of the language and a button to copy the contents of the code block:
 
-    ```js copy
+    ```javascript copy
     const copyMe = true
     ```