Fix ActiveModel::Errors#delete return value to stay backward compatible

Rails 5.0 changes to ActiveModel::Errors include addition of `details`
that also accidentally changed the return value of `delete`. Since
there was no test for that behavior it went unnoticed. This commit
adds a test and fixes the regression.

Small improvements to comments have also been made. Since `get` is
getting deprecated it is better to use `[]` in other methods' code
examples. Also, in the module usage example, `def Person.method`
was replaced with a more commonly used `def self.method` code style.

0 files changed, 0 insertions, 0 deletions