pandocYAMLHeader must use keepend ...

if matchgroup is not used

Author: lyokha

syntax/pandoc.vim

@@ -459,7 +459,7 @@ try
     syn include @YAML syntax/yaml.vim
 catch /E484/
 endtry
-syn region pandocYAMLHeader start=/\%(\%^\|\_^\s*\n\)\@<=\_^-\{3}\ze\n.\+/ end=/^\([-.]\)\1\{2}$/ contains=@YAML containedin=TOP
+syn region pandocYAMLHeader start=/\%(\%^\|\_^\s*\n\)\@<=\_^-\{3}\ze\n.\+/ end=/^\([-.]\)\1\{2}$/ keepend contains=@YAML containedin=TOP
 "}}}
 "}}}1