Fix grammar in manual

https://bugzilla.gnome.org/show_bug.cgi?id=779747

Author: haaninjo

help/C/folder-mode.page

@@ -221,7 +221,7 @@ files that have been <em>Modified</em>. You can read more about this in
 </p>
 
 <p>
-Finally, the most recently modified file/folder has an small star emblem
+Finally, the most recently modified file/folder has a small star emblem
 attached to it.
 </p>
 </section>