Version bumps for non-rails gems (#3398)

* Update xpath to version 2.1.0

* Update aws-sdk to version 2.9.25

* Update oj to version 3.0.10

* Update brakeman to version 3.6.2

* Update rufus-scheduler to version 3.4.2

* Update doorkeeper to version 4.2.6

* Update rubocop to version 0.49.0