Add rule 'rails_migrations_pending'

[abraham-chan]

Add rule to fix a common Rails issue when running tests.

Rails source code that generates the message: https://github.com/rails/rails/blob/main/activerecord/lib/active_record/migration.rb#L152

Example output on my console:

abrahamchan [master] > bin/rspec     
Running via Spring preloader in process 35661
Migrations are pending. To resolve this issue, run:

        rails db:migrate RAILS_ENV=test
No examples found.

abrahamchan [master] > fuck
rails db:migrate RAILS_ENV=test [enter/↑/↓/ctrl+c]
== 20210627174953 Example: migrating ==========================================
== 20210627174953 Example: migrated (0.0000s) =================================

abrahamchan [master] > bin/rspec
[successful rspec output]

[scorphus]

Looks good. Thanks.

Please consider my sugestion below.

[scorphus]

Reviewing it again, I thought that the corrected command could include the one initially intended by the user.

Suggested change

	(Command("", output_env_development), "rails db:migrate RAILS_ENV=development"),
	(Command("", output_env_test), "bin/rails db:migrate RAILS_ENV=test"),
	(Command("bin/rspec", output_env_development), "rails db:migrate RAILS_ENV=development && bin/rspec"),
	(Command("bin/rspec", output_env_test), "bin/rails db:migrate RAILS_ENV=test && bin/rspec"),

Make sure to use shell._and to join the commands together.

[abraham-chan]

Thanks, done

[scorphus]

Good job, @abraham-chan! Thanks for contributing!