[Danger] Use the markdown method to display the CHANGELOG format

Dangerfile

@@ -12,11 +12,12 @@ warn("Big PR") if git.lines_of_code > 500
 if !git.modified_files.include?("CHANGELOG.yml") && !declared_trivial
   fail("Please include a CHANGELOG entry. \nYou can find it at [CHANGELOG.md](https://github.com/SwiftGen/SwiftGen/blob/master/CHANGELOG.md).")
   changelog_msg = <<-CHANGELOG_FORMAT.gsub(/^ *\|/,'')
-  |We use the following format for CHANGELOG entries:
-  |<code><pre>
-  | * Describe your change here.  Don’t forget to use 2 spaces at the end of the last line describing your change.  
+  |Note: we use the following format for CHANGELOG entries:
+  |```
+  | * Describe your change here. Don’t forget to use 2 spaces at the end
+  |   of the last line describing your change.  
   |   [#nn](https://github.com/SwiftGen/SwiftGen/pull/nn)
-  |</pre>/<code>
+  |```
 CHANGELOG_FORMAT
-  message(changelog_msg)
+  markdown(changelog_msg)
 end