PGF web service: Use Content-Type text/javascript from JSON output

The Content-Type used to be text/json, but this caused warning messages in
some web browers.

src/server/FastCGIUtils.hs

@@ -165,7 +165,7 @@ outputJSONP x =
        let str = case mc of
                    Nothing -> encode x
                    Just c  -> c ++ "(" ++ encode x ++ ")"
-       setHeader "Content-Type" "text/json; charset=utf-8"
+       setHeader "Content-Type" "text/javascript; charset=utf-8"
        outputStrict $ UTF8.encodeString str
 
 outputPNG :: BS.ByteString -> CGI CGIResult