Upgrade Mongoid specs to RSpec 3 expect syntax

spec/mongoid/adapters/mongoid/base_spec.rb

@@ -20,7 +20,9 @@ module Ransack
 
           context 'with scopes' do
             before do
-              Person.stub :ransackable_scopes => [:active, :over_age]
+              allow(Person).to receive_messages(
+                ransackable_scopes: [:active, :over_age, :of_age]
+                )
             end
 
             it "applies true scopes" do

spec/mongoid/nodes/condition_spec.rb

@@ -26,7 +26,7 @@ module Ransack
             Ransack.configure { |config| config.ignore_unknown_conditions = true }
           end
 
-          specify { subject.should be_nil }
+          specify { expect(subject).to be_nil }
         end
       end
     end