Upgrade ruby to 2.3.1

.ruby-version

-ruby-2.2.4
+2.3.1

.travis.yml

@@ -18,7 +18,7 @@ addons:
   postgresql: 9.4
 
 rvm:
-  - 2.2.4
+  - 2.3.1
 
 services:
   - redis-server

Dockerfile.app

-FROM ruby:2.2.4
+FROM ruby:2.3.1
 
 ENV RAILS_ENV=production
 

spec/services/reblog_service_spec.rb

@@ -8,9 +8,7 @@ RSpec.describe ReblogService do
   subject { ReblogService.new }
 
   before do
-    Rails.configuration.x.hub_url = 'http://hub.example.com'
-
-    stub_request(:post, 'http://hub.example.com')
+    stub_request(:post, Rails.configuration.x.hub_url)
     stub_request(:post, 'http://salmon.example.com')
 
     subject.(alice, status)
@@ -21,7 +19,7 @@ RSpec.describe ReblogService do
   end
 
   it 'pings PubSubHubbub hubs' do
-    expect(a_request(:post, 'http://hub.example.com')).to have_been_made
+    expect(a_request(:post, Rails.configuration.x.hub_url)).to have_been_made
   end
 
   it 'sends a Salmon slap for a remote reblog' do