Update fetch.bs

Co-authored-by: Anne van Kesteren <annevk@annevk.nl>

fetch.bs

@@ -2690,7 +2690,7 @@ functionality.
 <a for=/>fetch controller</a> or null).
 
 <p>A <dfn export>deferred fetch record</dfn> is a <a for=/>struct</a> used to maintain state needed
-to invoke a fetch at a later time, e.g. when a <code>Document</code> is unloaded or backgrounded. It
+to invoke a fetch at a later time, e.g., when a <code>Document</code> is unloaded or backgrounded. It
 has the following <a for=struct>items</a>:
 
 <dl>