Update Oktakit.new convenience method for Ruby 3

Add spec to ensure it is working

Hash and keyword coercion was deprecated in Ruby 3 w/ warnings in Ruby 2.7.
See https://www.ruby-lang.org/en/news/2019/12/12/separation-of-positional-and-keyword-arguments-in-ruby-3-0/ for additional information or my post detailing it in https://medium.com/building-rigup/hash-and-keyword-coercion-213425f69719

lib/oktakit.rb

@@ -2,7 +2,7 @@
 require 'oktakit/client'
 
 module Oktakit
-  def self.new(*args)
-    Client.new(*args)
+  def self.new(**args)
+    Client.new(**args)
   end
 end

spec/oktakit_spec.rb

@@ -5,6 +5,13 @@
     expect(Oktakit::VERSION).not_to(be(nil))
   end
 
+  describe '.new' do
+    it 'creates a client with the passed in keyword arguments' do
+      client = Oktakit.new(token: test_okta_token, organization: 'okta-test')
+      expect(client.api_endpoint).to(eq('https://okta-test.okta.com/api/v1'))
+    end
+  end
+
   describe 'client' do
     it 'has a default API endpoint' do
       client = Oktakit::Client.new(token: test_okta_token, organization: 'okta-test')