Add krita-devel 4.0.0-prealpha (#4059)

* Add krita-devel 4.0.0-prealpha

* Update and rename krita-devel.rb to krita-dev.rb

Casks/krita-dev.rb

@@ -0,0 +1,14 @@
+cask 'krita-dev' do
+  version '4.0.0-prealpha'
+  sha256 'f63313ea07fcc1329d4d696153c5d6877940e5a23ec77d432075bd2e88fbe274'
+
+  # download.kde.org/unstable/krita was verified as official when first introduced to the cask
+  url "http://download.kde.org/unstable/krita/#{version}/krita-#{version}.dmg"
+  name 'Krita'
+  homepage 'https://krita.org/'
+
+  conflicts_with cask: 'krita'
+  depends_on macos: '>= :mavericks'
+
+  app 'Krita.app'
+end