Remove pinned prettier version, fix related linting inconsistencies

[bantic]

As pointed out here (https://github.com/Addepar/ember-table/pull/790#issuecomment-560470564), it looks like we may have incompatible linting happening at CI. To close this issue, remove the resolution of prettier from yarn.lock and upgrade deps or otherwise fix things so that all the linting that happens at CI passes.