Add "canvas" as a container tag

Author: christophermaier

src/hiccup/core.clj

@@ -60,7 +60,7 @@
 
 (def ^{:doc "A list of tags that need an explicit ending tag when rendered." :private true}
   container-tags
-  #{"a" "b" "body" "dd" "div" "dl" "dt" "em" "fieldset" "form" "h1" "h2" "h3"
+  #{"a" "b" "body" "canvas" "dd" "div" "dl" "dt" "em" "fieldset" "form" "h1" "h2" "h3"
     "h4" "h5" "h6" "head" "html" "i" "iframe" "label" "li" "ol" "option" "pre" 
     "script" "span" "strong" "style" "textarea" "ul"})