Errors encountered when migrating a table with generated columns

[iamadalek]

Receive the following error when running any migrations against a table that has generated columns:

The value specified for generated column 'sample_generated_column' in table 'lhmn_sample_table' is not allowed.

I believe that this is because the migrator attempts to write values into the generated column which is not allowed.

I created a PR that I think addresses the problem by excluding generated columns when writing: #141