Replace image 'url' with 'destination' (#512)

ph1ll · jgm · commit ba0855b3ef14 · 2018-03-25T16:19:00.000-07:00
diff --git a/CommonMark.dtd b/CommonMark.dtd
@@ -67,7 +67,7 @@
 
 <!ELEMENT image (%inline;)*>
 <!ATTLIST image
-          url CDATA #REQUIRED
+          destination CDATA #REQUIRED
           title CDATA #IMPLIED>
 
 <!ELEMENT html_inline (#PCDATA)>
