[web-animations-1] Fix link to document conventions

Author: birtles

web-animations-1/Overview.bs

@@ -448,7 +448,7 @@ refer to updating the property directly <em>without</em> invoking any related
 procedure.
 
 Further documentation conventions that are not specific to this specification
-are described in [[#document-conventions]].
+are described in [[#conventions]].
 
 Web Animations model overview {#web-animations-model-overview}
 =======================================