Fix SHA256 checksum for nginx 1.4.4

I'm not sure what's going on here, but the SHA-256 checksum I calculate for http://nginx.org/download/nginx-1.4.4.tar.gz using `sha256sum` on Ubuntu 14.04.1 is `7c989a5`, rather than the `0510af7` in `source.rb`:

    $ wget http://nginx.org/download/nginx-1.4.4.tar.gz
    $ sha256sum ./nginx-1.4.4.tar.gz
    7c989a58e5408c9593da0bebcd0e4ffc3d892d1316ba5042ddb0be5b0b4102b9  ./nginx-1.4.4.tar.gz
    
    $ ls -l /var/chef/cache/nginx-1.4.4.tar.gz
    ... Jun  4  2014 /var/chef/cache/nginx-1.4.4.tar.gz
    $ sha256sum /var/chef/cache/nginx-1.4.4.tar.gz 
    7c989a58e5408c9593da0bebcd0e4ffc3d892d1316ba5042ddb0be5b0b4102b9  /var/chef/cache/nginx-1.4.4.tar.gz

Recently a chef-client run threw a fatal error that the checksum was incorrect. However I still have the cached downloaded resource from June 2014 and the file is the same, `7c989a5`. So did this only recently begin being checked, or is it some other issue on my end? How was the checksum "wrong" this whole time but only recently threw the error?