fix: files ls inconsisntency
It is stated on interface-ipfs-core that files.ls type's must be strings (file or directory).
Tests: https://github.com/ipfs/interface-ipfs-core/pull/282
@alanshaw what do you think about this?
@alanshaw what's the state of this PR? The same for https://github.com/ipfs/interface-js-ipfs-core/pull/282
@hacdias did you see the comments here https://github.com/ipfs/interface-js-ipfs-core/pull/282#discussion_r232642237 ?
@alanshaw I believe I missed it!! Just read the comments. I'll work on those points. I'll close this PR as soon as I open a new one since this is a bit out of date.