Append newlines to `ipfs id` and `ipfs dns` output.

This fixes #1083, #2000.

N.B. The JSON package developers see no trailing newline as a feature;
it allows marshalled JSON to be embedded inside more JSON.[0]

--
[0] https://golang.org/pkg/encoding/json/



License: MIT
Signed-off-by: Thomas Gardner <tmg@fastmail.com>