DEP Use carets instead of dev requirements and use phpunit 9

[emteknetnz]

Issue https://github.com/silverstripeltd/product-issues/issues/497

Now that CWP won't be getting regular releases via cow, it probably makes sense to change this to carets to support adhoc releases

[emteknetnz]

^ broken travis test is phpunit9 related - fix is to tag 2.9.0 (new minor) of cwp-core - https://github.com/silverstripe/cwp-core/pull/101/files

@maxime-rainville this might be a bit weird, particularly as that requires framework ^4.10 which is unreleased - may make sense to just merge this with broken unit test?

[maxime-rainville]

@emteknetnz Do you want to do a new cwp-core tag. It seemed to work for the other module?

[emteknetnz]

@maxime-rainville tagged cwp-core 2.9.0 and rerunning the build on this

[emteknetnz]

Unit test requires silverstripe/admin 4.10/4.x-dev due to phpunit 9

Requirement for admin would need to be updated in to ^4.10 in
https://github.com/silverstripe/cwp-core/blob/2/composer.json

However I tagged cwp-core 2.9.0 just the other day, probably a little excessive tagged 2.10 days later - might make sense to just remove the tag and retag - though this would require us deleting the tag in packagist as well which I don't have enough permissions to do https://packagist.org/packages/cwp/cwp-core#2.9.0

Other option is just tag 2.9.1, though I'm not sure if that's semver correct

[maxime-rainville]

I'm fine tagging 2.9.1. As a general rule, we should never undo a tag.

[emteknetnz]

Cool - PR silverstripe/cwp-core#104

[maxime-rainville]

LGTM and build are green.