Added firefox-nl.rb as requested

Requested by gmkey here
https://github.com/caskroom/homebrew-cask/issues/11367

Casks/firefox-nl.rb

@@ -0,0 +1,18 @@
+cask :v1 => 'firefox-nl' do
+  version :latest
+  sha256 :no_check
+
+  url 'https://download.mozilla.org/?product=firefox-latest&os=osx&lang=nl'
+  name 'Firefox'
+  name 'Mozilla Firefox'
+  homepage 'https://www.mozilla.org/nl/firefox/desktop'
+  license :mpl
+  tags :vendor => 'Mozilla'
+
+  app 'Firefox.app'
+
+  zap :delete => [
+                  '~/Library/Application Support/Firefox',
+                  '~/Library/Caches/Firefox',
+                 ]
+end