Users table is not compatible with MySQL 5.7

[rporres]

When trying to initialise the database we get (formatted)

Mysql2::Error: All parts of a PRIMARY KEY must be NOT NULL; if you need NULL in a key, use UNIQUE instead: 
CREATE TABLE `users` (
`id` int(11) DEFAULT NULL auto_increment PRIMARY KEY, 
`username` varchar(255) DEFAULT '' NOT NULL, 
`email` varchar(255) DEFAULT '' NOT NULL,
 `encrypted_password` varchar(255) DEFAULT '' NOT NULL, 
`reset_password_token` varchar(255),
`reset_password_sent_at` datetime,
 `remember_created_at` datetime,
 `sign_in_count` int(11) DEFAULT 0,
 `current_sign_in_at` datetime,
 `last_sign_in_at` datetime,
 `current_sign_in_ip` varchar(255), 
`last_sign_in_ip` varchar(255),
 `created_at` datetime NOT NULL, 
`updated_at` datetime NOT NULL) ENGINE=InnoDB
/usr/lib/ruby/gems/1.9.1/gems/mysql2-0.3.21/lib/mysql2/client.rb:85:in `_query'
/usr/lib/ruby/gems/1.9.1/gems/mysql2-0.3.21/lib/mysql2/client.rb:85:in `query'

The problem is 5.7 no longer supporting null values for the primary key.

https://dev.mysql.com/doc/refman/5.7/en/create-table.html#create-table-indexes-keys

A unique index where all key columns must be defined as NOT NULL. If they are not explicitly declared as NOT NULL, MySQL declares them so implicitly (and silently). A table can have only one PRIMARY KEY.