Skip certificates:install if KEY_PASSWORD does not exists.

[ci skip]

Rakefile

@@ -46,4 +46,10 @@ if ENV["KEY_PASSWORD"]
     t.add_certificate('./certificates/AppleWWDRCA.cer')
     t.add_certificate('./certificates/development.p12', ENV["KEY_PASSWORD"])
   end
+else
+  namespace :certificates do
+    task :install do
+      puts "skip certificates:install because KEY_PASSWORD does not exists."
+    end
+  end
 end