support after Rails 4.2.0.rc1

Renamed instance variable `table_name` to `name` after Rails version 4.2.0.rc1, and Table#name accessor is added.
So enable both of Rails version under 4.2.0.beta4 and over 4.2.0.rc1.

SEE ALSO: https://github.com/rails/rails/commit/76e7305ea16b41a3674f4213ab7faa8c65196d75