Upgraded migrations plugin for cakephp 3.0

Is it okay sending pull request to develop branch?
If you have any request, feel free to ask me :)

I've also sent pull request to cakephp 3.0 core, since it's db layer classes are currently broken and there seems to be a lot more changes are going to made. (e.g. removal of Model class, ConnectionManager::getDataSource() deprecation )
https://github.com/cakephp/cakephp/pull/2396

Though it's currently working for my project in my use, perhaps this change set will be broken in near future. Hopefully this request to be the first step for upgrade.