Small improvements to tighten up the APIs

• style: removed unused imports 78a3686
• feat: allow request.plainCookie options to be set via an object 9a1307c
• feat: add response helpers to inspect the type of response body 419c16c
• fix: remove header on Node.js res object via "response.removeHeader" 3fb7afc
• chore: update dependencies 870fac8

Full Changelog: v6.5.0-0...v6.6.0-0