Update mime.types with proper javascript type

`application/x-javascript` should be `application/javascript` per the RFC and official nginx config
see: http://trac.nginx.org/nginx/changeset/ae3fd1ca62e0942a6c83a37f30df386622462c80/nginx
and: http://www.rfc-editor.org/rfc/rfc4329.txt

This also fixes default config to work with default charset_types.