Wordpress prompting for FTP credentials - Ubuntu 14.04 / LAMP configuration

I followed the Digital Ocean tutorial for configuring secure updates for Wordpress using SSH keys and I am still being prompted for the FTP information when I try to install at new theme.

In the wp-config.php file I added:

define('FS_METHOD', 'direct');
define('FTP_PUBKEY','/home/wp-user/.ssh/wp_rsa.pub');
define('FTP_PRIKEY','/home/wp-user/.ssh/wp_rsa');
define('FTP_USER','wp-user');
define('FTP_PASS','wp-pass');
define('FTP_HOST','127.0.0.1:22');

Where wp-user and wp-pass have been replaced by the appropriate user name and password. The FS_METHOD line wasn’t in the tutorial, but something I saw suggested for related problems, e.g. here and here.

The permissions on the files are:

-rw-r--r-- 1 wp-user wp-user      755 Jul 16 21:03 authorized_keys
-rw-r----- 1 wp-user www-data 3326 Jul 16 20:57 wp_rsa
-rw-r----- 1 wp-user wp-user      738 Jul 16 21:00 wp_rsa.pub

The permissions on the ~/.ssh, var/www, :

drwx------ 2 wp-user wp-user    4096 Jul 16 21:03 .ssh

...

drwxrwxr-x  3 wp-user www-data 4096 Jul 13 13:51 www

I also prepended the RSA information in the authorized_keys file with from="127.0.0.1" and restarted apache with sudo service apache2 restart more times than I care to admit.

Is there anything else I should be doing?

Thank you!