add enabled? to authenticator (to prevent warnings)

lib/mozilla_iam/authenticator.rb

@@ -1,5 +1,10 @@
 module MozillaIAM
   class Authenticator < Auth::OAuth2Authenticator
+
+    def enabled?
+      true
+    end
+
     def after_authenticate(auth_token)
       begin
         id_token = auth_token[:credentials][:id_token]

spec/components/mozilla_iam/authenticator_spec.rb

@@ -1,6 +1,13 @@
 require_relative '../../iam_helper'
 
 describe MozillaIAM::Authenticator do
+
+  context "#enabled?" do
+    it "returns true" do
+      expect(described_class.new('auth0', trusted: true).enabled?).to be true
+    end
+  end
+
   context '#after_authenticate' do
     it 'can authenticate a new user' do
       user = {