update version references to 1.0.0-beta.4

[philvarner]

Related Issue(s): n/a

Proposed Changes:

1. Update version references to 1.0.0-beta.4, since we know what the next version is going to be.

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)
• I have added my changes to the CHANGELOG or a CHANGELOG entry is not required.

[m-mohr]

Haven't we just releaed beta.3 some days ago? :-o

[philvarner]

Haven't we just releaed beta.3 some days ago? :-o

Yes, but I was going to try to start updating this at the beginning of the milestone cycle rather than the end.

[m-mohr]

Don't forget the CHANGELOG updates later ;-)