whoops! pass down force argument to installer

this was preventing the `brew cask install --force cask` syntax from
working

the test was wrong too - corrected that so now we're covered from future
breakage

refs #329

lib/cask/cli/install.rb

@@ -5,7 +5,7 @@ class Cask::CLI::Install
     cask_names.each do |cask_name|
       begin
        cask = Cask.load(cask_name)
-       Cask::Installer.install(cask)
+       Cask::Installer.install(cask, force)
        Cask::AppLinker.new(cask).link
        Cask::PkgInstaller.new(cask).install
       rescue CaskError => e

test/cli/install_test.rb

@@ -29,7 +29,7 @@ describe Cask::CLI::Install do
 
     TestHelper.must_output(self, lambda {
       Cask::CLI::Install.run('local-transmission', '--force')
-    }, 'Error: Cask for local-transmission is already installed. Use `--force` to install anyways.')
+    }, /Success! local-transmission installed/)
   end
 
   it "properly handles casks that are not present" do