chore: unnecessary use of fmt.Sprintf

[testwill]

Reason for the change If applicable, link the related issue/bug report or write down in few sentences the motivation.

Description unnecessary use of fmt.Sprintf

Code examples If applicable, add code examples to help explain your changes.

Checklist

• [ ] I have read and agreed to the RethinkDB Contributor License Agreement

References Anything else related to the change e.g. documentations, RFCs, etc.

[gabor-boros]

@testwill Thank you for the contribution. Could you please accept the CLA to be able to merge this?