Coordinate release support with altis/cms

[goldenapples]

Currently the altis-cms package is requiring ^0.6.4 of this plugin:
https://github.com/humanmade/altis-cms/blob/master/composer.json#L18

This means that the latest releases (0.7.0, 0.7.1, and 0.8.0) can't be used in projects hosted on Altis.

I don't think there are any changes in 0.7.x or 0.8.x that break backwards-compatability. I'd like to investigate getting support added for the latest versions in the altis packages.

[goldenapples]

Opened humanmade/altis-cms#941 in the altis-cms repo to coordinate.

[kadamwhite]

Noting that we anticipate releasing a 1.0 today or tomorrow which adds even more methods. Some methods have been deprecated in 0.8.0 but we don't anticipate removing them in 1.0, as of right now, so we can probably bump the version range even further to include ^1.0 once the new release is out.