Add version numbers to pre-5.0 Ruby on Rails ActiveRecord migrations.

add_versions_to_old_migrations.rb

# Run from db/migrate to fix your old un-versioned migrations, so that they don't break on Rails 5.1

Dir.glob('*').each do |migration|
  versioned_migration = File.read(migration).gsub("< ActiveRecord::Migration\n", "< ActiveRecord::Migration[4.2]\n")
  File.open(migration, 'w') do |output|
    output << versioned_migration
  end
end