linting fix: replace lazy '==' with more strict '==='

Most of these were string comparisons, so the change shouldn't be risky. 

The only one I'd really liked looked at is https://github.com/FredKSchott/request/compare/mikeal:master...FredKSchott:linting-fix-eqeqeq?expand=1#diff-ccc0734f65dd7a299409ff07d35be095R1267 where we were checking for `null`, but it sounds like we really meant to be checking for `undefined`. Both passed with the lazy comparison, but now we only check for undefined. If we'd like to check for both, lets replace this line with `if (!body)` instead.