Remove 'text/html' from nginx gzip config to get rid of warning message. See http://wiki.nginx.org/HttpGzipModule#gzip_types

$ sudo service nginx start

nginx: [warn] duplicate MIME type "text/html" in /etc/nginx/nginx.conf:26
Merge pull request #335 from johnnyshields/nginx-warning

Remove 'text/html' from nginx gzip config to get rid of warning message.