Add support for JSON output

[coderpatros]

In preparation of v1.2 of the spec we need to support JSON output.

[manuel-sommer]

This can be closed due to the merge.

[rahearn]

Is there a timeline for when JSON support will be released to rubygems?

[pidj]

Hi @coderpatros, can I relaunch the query of rahearn please ? We would be very interested to this new version published on the rubygems public repo. The current latest version there doesn't support the JSON format yet. Thanks in advance !