Collections list is just plain JSON

[tschaub]

Proposed Changes:

1. Update example link type to be application/json instead of application/geo+json for collections list.

PR Checklist:

• This PR is made against the dev branch (all proposed changes except releases should be against dev, not master).
• This PR has no breaking changes.
• This PR does not make any changes to the core spec in the stac-spec directory (these are included as a subtree and should be updated directly in radiantearth/stac-spec)
• A CHANGELOG entry is not required (I don't think).

[philvarner]

CI is broken right now because of #301 , that needs to be resolved before we can merge. (it's an easy fix, someone just needs to do it)

[tschaub]

#302 updates the openapi.yaml to use booleanExpression

[philvarner]

updated this to be against dev instead of master