[cssom][cssom-view] Meta: use <script async> for file-issue.js

Author: zcorpan

cssom-view/Overview.bs

@@ -91,7 +91,7 @@ spec:dom; type:interface; text:Document
 spec:html; type:dfn; text:case-sensitive
 </pre>
 
-<script src=https://resources.whatwg.org/file-issue.js defer data-file-issue-url="https://github.com/w3c/csswg-drafts/issues/new?title=%5Bcssom-view%5D%20"></script>
+<script src=https://resources.whatwg.org/file-issue.js async data-file-issue-url="https://github.com/w3c/csswg-drafts/issues/new?title=%5Bcssom-view%5D%20"></script>
 
 Background {#background}
 ========================

cssom/Overview.bs

@@ -111,7 +111,7 @@ spec:css-logical-props-1; type:property; text:inline-size
 spec:css-variables-1; type:dfn; text:custom property
 </pre>
 
-<script src=https://resources.whatwg.org/file-issue.js defer data-file-issue-url="https://github.com/w3c/csswg-drafts/issues/new?title=%5Bcssom%5D%20"></script>
+<script src=https://resources.whatwg.org/file-issue.js async data-file-issue-url="https://github.com/w3c/csswg-drafts/issues/new?title=%5Bcssom%5D%20"></script>
 
 Introduction {#introduction}
 ============================