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 use case, perhaps this change set will be broken in near future. Hopefully this request to be the first step for upgrade.