This gem catches the following unsafe migrations:
     - adding a column with a non-null default value to an existing table
     - changing the type of a column
     - renaming a table
     - renaming a column
     - removing a column
     - adding an index non-concurrently (Postgres only)
     - adding a json column to an existing table (Postgres only)

WWW: https://github.com/ankane/strong_migrations