[Delivers ###163460580] Revise approach to correcting response-body encoding
[Delivers ###163460580] Revise approach to correcting response-body encoding

Prior Commit incorrectly relied on content_type.
Instead:
- Use the previously ignored and undocumented encoding argument to the method;
- Document how that argument is used
- Document reason for fixing response-body encoding.
- Trivial Rubocopping

See generally https://mushroomobserver.slack.com/archives/C040TH9FV/p1548529248006300, et seq.

JoeCohen/mushroom-observer,MushroomObserver/mushroom-observer,JoeCohen/mushroom-observer,MushroomObserver/mushroom-observer,JoeCohen/mushroom-observer,MushroomObserver/mushroom-observer,pellaea/mushroom-observer,pellaea/mushroom-observer,pellaea/mushroom-observer,MushroomObserver/mushroom-observer,JoeCohen/mushroom-observer,JoeCohen/mushroom-observer,JoeCohen/mushroom-observer,JoeCohen/mushroom-observer,pellaea/mushroom-observer,pellaea/mushroom-observer,MushroomObserver/mushroom-observer,pellaea/mushroom-observer,pellaea/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer