Refactor `main_adapter#add_spatial_column` method signature

This PR simplifies the signature of  `main_adapter#add_spatial_column` as discussed in https://github.com/rgeo/activerecord-postgis-adapter/pull/121. There may be cleaner ways of dealing with the data we need from `info` but with this implementation the logic is unchanged.

  * Remove `info` from signature
  * Include `minitest/pride` in tests because colors are nice