Add miniconda2 for python 2.x (#3516)

* Add miniconda2 for python 2.x

Adds miniconda2 by Continuum Analytics.

This differs from @drzax's [miniconda](https://github.com/caskroom/homebrew-cask/blob/master/Casks/miniconda.rb) in that it is for python 3.x. miniconda2 is for python 2.x.

Follows the same versioning logic as

* Rename miniconda2 to miniconda2.rb

Casks/miniconda2.rb

@@ -0,0 +1,21 @@
+cask 'miniconda2' do
+  version :latest
+  sha256 :no_check
+
+  url 'https://repo.continuum.io/miniconda/Miniconda2-latest-MacOSX-x86_64.sh'
+  name 'Continuum Analytics Miniconda'
+  homepage 'https://www.continuum.io/why-anaconda'
+
+  auto_updates true
+  depends_on macos: '>= :lion'
+  container type: :naked
+
+  installer script: 'Miniconda2-latest-MacOSX-x86_64.sh',
+            args:   ['-b']
+
+  uninstall delete: '~/miniconda2'
+
+  caveats do
+    path_environment_variable '~/miniconda2/bin'
+  end
+end