[css-variables-1] Changed id=cssom to id=apis, because Bikeshed generated a duplicate ID. (Bug in Bikeshed?)

Author: bert-github

css-variables/Overview.bs

@@ -1,6 +1,7 @@
 <h1>CSS Custom Properties for Cascading Variables Module Level 1</h1>
 
 <pre class='metadata'>
+!Date: 2014-05-06
 Status: ED
 Shortname: css-variables
 Level: 1
@@ -615,7 +616,7 @@ AAAAAAA                   AAAAAAAPPPPPPPPPP          IIIIIIIIII
 -->
 
 
-<h2 id='cssom'>
+<h2 id='apis'>
 APIs</h2>
 
 	All <a>custom property</a> <a>declarations</a> have the <a>case-insensitive</a> flag set.