Merge pull request #1078 from HonkingGoose/patch-1

Add missing % at the end of a template example

Author: janiceilene

contributing/content-markup-reference.md

@@ -64,7 +64,7 @@ Octicons are icons used across GitHub’s interface. We reference Octicons when
 
 `{% octicon "<name of octicon>" %}`  
 `{% octicon "plus" %}`
-`{% octicon "plus" aria-label="The plus icon"}`
+`{% octicon "plus" aria-label="The plus icon" %}`
 
 ## Operating system tags