Fixes for tests to run under rspec3

spec/builder_spec.rb

@@ -148,7 +148,7 @@ def encode_as_json
 
   describe "attributes!" do
     it "should allow create object with attributes of another object" do
-      object = stub(:id => 1, :name => 'foo')
+      object = double(:id => 1, :name => 'foo')
       json.attributes!(object, :id, :name)
       MultiJson.load(json.compile!).should == {'id' => 1, 'name' => 'foo'}
     end

spec/jsonify_spec.rb

@@ -1,4 +1,4 @@
 require 'spec_helper'
 describe Jsonify do
-  it('should be true') {true.should be_true}
-end
+  it('should be true') {expect(true).to be true}
+end

spec/spec_helper.rb

@@ -6,4 +6,5 @@
 require 'jsonify/tilt'
 
 RSpec.configure do |config|
-end
+  config.expect_with(:rspec) { |c| c.syntax = [:should, :expect] }
+end