gem: add sorbet support

spec/daemon_spec.rb

@@ -1,3 +1,4 @@
+# typed: false
 require 'spec_helper'
 
 describe Dyndnsd::Daemon do

spec/spec_helper.rb

@@ -1,3 +1,4 @@
+# typed: strong
 
 require 'rubygems'
 require 'bundler/setup'

spec/support/dummy_database.rb

@@ -1,3 +1,4 @@
+# typed: true
 
 require 'forwardable'
 

spec/support/dummy_updater.rb

@@ -1,3 +1,4 @@
+# typed: true
 
 module Dyndnsd
   module Updater