add from cms distro is installing non-stable (alpha/beta) releases

[andrew-c-tran]

What happened (or feature request):

Add from CMS Distro downloads and installs the most latest versions of the CMS selected. However, it was discovered that it pulls the latest versions regardless of if they're stable or not.

What you expected to happen:

DDEV-UI should only use stable (non-alpha/beta/etc) releases.

Related source links or issues:

Discovered in #70

Please use a complexity rating of 1-5 (5 is high) for a feature request. (High complexity implies more PR planning)

1

[rickmanelius]

FWIW, this is nice but not urgent. Probably post v0.3

[rickmanelius]

Note that this is only for Drupal 8 (D7 and WP seem to be using stable releases). It would be great to address, but not urgent.