[Bug fix] update name mapping in Transaction.update_schema

[sungwy]

Also update name mapping if schema is updated through a Transaction.

Related PR

This PR fixes the current behavior, which only updates the name mapping if UpdateSchema is created from the Table.update_schema function. Transaction.update_schema should also pass the name_mapping of the table.

    with simple_table.transaction() as txn:
        with txn.update_schema() as schema_update:
            schema_update.rename_column("bar", "var")

[HonahX]

LGTM! Thanks for fixing this @syun64

[HonahX]

Remove this from 0.6.1 because this depends on #441, which is a new feature.