use v4 for auth:whoami

lib/heroku/command/auth.rb

@@ -77,10 +77,7 @@ def token
   # [email protected]
   #
   def whoami
-    validate_arguments!
-
-    display Heroku::Auth.user
+    Heroku::JSPlugin.setup
+    Heroku::JSPlugin.run('whoami', nil, ARGV[1..-1])
   end
-
 end
-

spec/heroku/command/auth_spec.rb

@@ -23,16 +23,4 @@
 STDOUT
     end
   end
-
-  describe "auth:whoami" do
-    it "displays the user's email address" do
-      stderr, stdout = execute("auth:whoami")
-      expect(stderr).to eq("")
-      expect(stdout).to eq <<-STDOUT
-[email protected]
-STDOUT
-    end
-
-  end
-
 end