brew-cask.rb: use 1.8-valid syntax (#22646)

The `key: value` syntax wasn't introduced until 1.9.

Causing a failure here: https://travis-ci.org/Homebrew/homebrew-emacs/jobs/142633016#L284

.rubocop.yml

@@ -40,6 +40,10 @@ Metrics/ModuleLength:
 Style/ClassAndModuleChildren:
   EnforcedStyle: compact
 
+Style/HashSyntax:
+  Exclude:
+    - 'brew-cask.rb'
+
 Style/PredicateName:
   NameWhitelist: is_32_bit?, is_64_bit?
 

brew-cask.rb

@@ -1,8 +1,8 @@
 class BrewCask < Formula
   homepage "https://github.com/caskroom/homebrew-cask/"
-  url "https://github.com/caskroom/homebrew-cask.git", tag: "v0.60.1"
+  url "https://github.com/caskroom/homebrew-cask.git", :tag => "v0.60.1"
 
-  depends_on ruby: "2.0"
+  depends_on :ruby => "2.0"
 
   UNINSTALL_MSG = <<-EOS.undent
     You must uninstall this formula. It is no longer needed to stay up to date,