fix: only accept cid for ipfs.dag.get

[achingbrain]

If you have a path within the DAG to resolve, pass it as path in the options object.

Makes the API conform to the documentation.

Fixes #3637

[rvagg]

Travis is failing because examples/traverse-ipld-graphs/eth.js is passing string CIDs, I guess we don't have type checking extending down into there too?

[vasco-santos]

LGTM

[achingbrain]

I guess we don't have type checking extending down into there too?

This is intentional - the idea is to show a single idea as simply as possible and to not make any other technical decisions for the user, e.g. just plain js as far as possible, as they'll likely copy/paste example code into their own app so we don't want them to then have to remove extra scaffolding or framework code etc.

[CSDUMMI]

Travis is failing because examples/traverse-ipld-graphs/eth.js is passing string CIDs, I guess we don't have type checking extending down into there too?

@rvagg the issue still exists in the release. #3689

[CSDUMMI]

I do not see, why we need to restrict the types.
This is a breaking change and not intuitive!

Because most js-IPFS functions (see Files API)
accept both CID and String.