Chore: bump `bundler` version to 2.1.2 (#409)
Chore: bump `bundler` version to 2.1.2 (#409)

* Bump bundler version to 1.16.6

Previous version: 1.14.6

* Update bundle version to 1.17.3

* Upgrade bundler to 2.1.2

The final version of 2019.

sendgrid/sendgrid-ruby,sendgrid/sendgrid-ruby