New cask: darktable-dev 3.0.0rc1 (#8192)
New cask: darktable-dev 3.0.0rc1 (#8192)

* New cask: darktable-dev 3.0.0rc1

* fix checksum, add conflict with stable cask

Signed-off-by: Yurii Kolesnykov <dc76e9f0c0006e8f919e0c515c66dbba3982f785@yurikoles.com>

caskroom/homebrew-versions,pkq/homebrew-versions,lantrix/homebrew-versions,mahori/homebrew-cask-versions,rogeriopradoj/homebrew-versions,lantrix/homebrew-versions,rogeriopradoj/homebrew-versions,404NetworkError/homebrew-versions,pkq/homebrew-versions,caskroom/homebrew-versions,404NetworkError/homebrew-versions