Add .NET Core SDK v2.0.0 Preview 2 (#4258)

* Add .NET Core SDK v2.0.0 Preview 2

* Update dotnet-sdk-preview.rb

* depends on openssl / sierra

Casks/dotnet-sdk-preview.rb

@@ -0,0 +1,18 @@
+cask 'dotnet-sdk-preview' do
+  version '2.0.0-preview2-006497'
+  sha256 'de675118efc09f80d4f2927b791b64806e7fbbd640b56d408b92d4e6ce4b167c'
+
+  url "https://download.microsoft.com/download/6/1/B/61B3E81F-5509-48D2-BB4F-5189E23CD29A/dotnet-sdk-#{version}-osx-x64.pkg"
+  name '.NET Core SDK Preview'
+  homepage 'https://www.microsoft.com/net/core/preview#macos'
+
+  depends_on formula: 'openssl'
+  depends_on macos: '>= :sierra'
+
+  pkg "dotnet-sdk-#{version}-osx-x64.pkg"
+
+  uninstall pkgutil: 'com.microsoft.dotnet*',
+            delete:  '/etc/paths.d/dotnet'
+
+  zap trash: '~/.nuget'
+end