Fix ipfs.ls() for a single file object

[ikreymer]

This fixes a typo where ipfs.ls() returns instead of yielding from a generator.
The result is that ipfs.ls() does not work when the path is a file. I think this should fix it, with ls returning a generator with a single file result.

(Note: I wanted to add a test but could not find where this command is being tested).

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[achingbrain]

Thanks for submitting this, great catch & the fix looks good.

The tests for this part of the API live here: https://github.com/ipfs/js-ipfs/blob/master/packages/interface-ipfs-core/src/ls.js - could you please add a test for this and I'll get a patch release out.

[achingbrain]

Thanks for adding the tests, I added a couple more and fixed up the breakage when invoking the api over http.