Don't include mathml javascript for html5 output.

mathml is supposed to be supported in HTML5.

README

@@ -544,10 +544,10 @@ Math rendering in HTML
     so it can be cached.
 
 `--mathml`[=*URL*]
-:   Convert TeX math to MathML (works with `docbook` as well as `html`).
-    In standalone mode, a small javascript (or a link to such a script if a
-    *URL* is supplied) will be inserted that allows the MathML to be viewed on
-    some browsers.
+:   Convert TeX math to MathML (in `docbook` as well as `html` and `html5`).
+    In standalone `html` output, a small javascript (or a link to such a
+    script if a *URL* is supplied) will be inserted that allows the MathML to
+    be viewed on some browsers.
 
 `--jsmath`[=*URL*]
 :   Use [jsMath] to display embedded TeX math in HTML output.

src/Text/Pandoc/Writers/HTML.hs

@@ -147,10 +147,11 @@ pandocToHtml opts (Pandoc (Meta title' authors' date') blocks) = do
                                        ! A.type_ "text/javascript"
                                        $ mempty
                            _ -> case lookup "mathml-script" (writerVariables opts) of
-                                      Just s ->
+                                      Just s | not (writerHtml5 opts) ->
                                         H.script ! A.type_ "text/javascript"
                                            $ preEscapedString
                                             ("/*<![CDATA[*/\n" ++ s ++ "/*]]>*/\n")
+                                             | otherwise -> mempty
                                       Nothing -> mempty
                 else mempty
   let newvars = [("highlighting-css",