Fix punctuation

Author: jungkees

dom.bs

@@ -1213,7 +1213,7 @@ and an <a>event listener</a> <var>listener</var>, set <var>listener</var>'s
 method, when invoked, must run these steps:
 
 <ol>
- <li><p>If the <a>context object</a> is a {{ServiceWorkerGlobalScope}} object, its associated
+ <li><p>If the <a>context object</a> is a {{ServiceWorkerGlobalScope}} object and its associated
  <a for="ServiceWorkerGlobalScope">service worker</a>'s <a for="service worker">set of event types
  to handle</a> contains <var>type</var>, then <a>report a warning to the console</a> with a
  description explaining that the user agent will still start the <a>service worker</a> for the