Update Rails to 4.2.10

Changes since 4.2.8:

- [No change in ActionMailer](https://github.com/rails/rails/blob/v4.2.10/actionmailer/CHANGELOG.md)
- [1 change and 1 regression fix in ActionPack](https://github.com/rails/rails/blob/v4.2.10/actionpack/CHANGELOG.md)
- [No change in ActiveModel](https://github.com/rails/rails/blob/v4.2.10/activemodel/CHANGELOG.md)
- [7 fixes in ActiveRecord](https://github.com/rails/rails/blob/v4.2.10/activerecord/CHANGELOG.md)
- [5 fixes in ActiveSupport](https://github.com/rails/rails/blob/v4.2.10/activesupport/CHANGELOG.md)
- [No change in Railties](https://github.com/rails/rails/blob/v4.2.10/railties/CHANGELOG.md

)

Signed-off-by: Rémy Coutable <remy@rymai.me>