Merge pull request commonmark#265 from github/remove-source-html-blocks

Remove `source` from list of HTML block elements

Author: lumaxis

changelog.txt

@@ -1,3 +1,6 @@
+[0.29.0.gfm.4]
+  * Remove `source` from list of HTML blocks
+
 [0.29.0.gfm.3]
   * Fixed heap memory corruption vulnerabiliy via integer overflow per https://github.com/github/cmark-gfm/security/advisories/GHSA-mc3g-88wq-6f4x