Fix lti-advantage gem specs and change activemodel version

Test Plan:
verify lti-advantage gem specs pass locally and
on Jenkins.

Change-Id: I8707914ec5dff77b275ddc92c951e8a865925ba5
Reviewed-on: https://gerrit.instructure.com/160124
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>

gems/lti-advantage/lib/lti_advantage/messages/jwt_message.rb

@@ -31,6 +31,7 @@ module LtiAdvantage::Messages
     }.freeze
 
     attr_accessor *REQUIRED_CLAIMS
+    attr_accessor *TYPED_ATTRIBUTES.keys
     attr_accessor :address,
                   :birthdate,
                   :custom,

gems/lti-advantage/lti-advantage.gemspec

@@ -30,7 +30,7 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
 
   spec.add_runtime_dependency 'json-jwt', '~> 1.5'
-  spec.add_runtime_dependency "activemodel", "~> 5.1.6"
+  spec.add_runtime_dependency "activemodel", "~> 5.1"
 
   spec.add_development_dependency "redcarpet"
   spec.add_development_dependency "bundler", "~> 1.16"

gems/lti-advantage/spec/lti_advantage/messages/resource_link_request_spec.rb

@@ -72,9 +72,9 @@ module LtiAdvantage::Messages
           context: LtiAdvantage::Claims::Context.new
         )
         message.validate
-        expect(message.errors.messages[:context]).to match_array [
-          { id: ["can't be blank"] }
-        ]
+        expect(message.errors.messages[:context].first.messages).to eq(
+          {:id => ["can't be blank"]}
+        )
       end
 
       it 'verifies that "aud" is an array' do

gems/lti-advantage/test.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+set -e
+
+bundle check || bundle install
+bundle exec rspec spec