Fix the assertion for not inclusion of turbolinks on application.js.

We were asserting if `//= turbolinks` was not present while the correct is
asserting that `//= require turbolinks` is not present.
Merge pull request #13003 from laurocaetano/fix_assertion_for_turbolinks

Fix the assertion for not inclusion of turbolinks on application.js.
Use a more generic assertion to make sure this tests will be useful.

Since we are using assert_no_match, if we change the code before
changing the tests, the tests will still pass and the assertion will
become useless
Fix validation on uniqueness of empty association
When Array#as_json and Hash#as_json are called without options, they
should also call #as_json on the children without options (instead of
nil)
Merge pull request #12774 from exAspArk/fix_uniqueness_on_relation

Fix validation on uniqueness
Merge pull request #13007 from chancancode/dont_call_as_json_with_nil

Don't call #as_json on children of Array and Hash with nil when no arguments are passed