switch rails caching from memcachier to heroku-redis

We don't really care between the two, and this should keep
all of our billing at Heroku (which can then be part of a
single sponsorship).

Gemfile

@@ -5,11 +5,10 @@ gem 'rails', '4.2.6'
 gem 'rails_12factor', group: :production
 
 gem 'asciidoctor', '>=1.5.4'
-gem 'dalli'
+gem 'redis-rails'
 gem 'exceptional'
 gem 'faraday'
 gem 'faraday_middleware'
-gem 'memcachier'
 gem 'octokit'
 gem "pg"
 gem 'rack-timeout'

Gemfile.lock

@@ -71,7 +71,6 @@ GEM
       compass (>= 0.12.2)
     crack (0.4.2)
       safe_yaml (~> 1.0.0)
-    dalli (2.7.2)
     database_cleaner (1.3.0)
     debug_inspector (0.0.2)
     debugger-linecache (1.2.0)
@@ -112,7 +111,6 @@ GEM
       nokogiri (>= 1.5.9)
     mail (2.6.3)
       mime-types (>= 1.16, < 3)
-    memcachier (0.0.2)
     mime-types (1.25.1)
     mini_portile2 (2.0.0)
     minitest (5.8.4)
@@ -163,6 +161,23 @@ GEM
     rdoc (4.1.1)
       json (~> 1.4)
     redcarpet (3.2.3)
+    redis (3.3.3)
+    redis-actionpack (5.0.1)
+      actionpack (>= 4.0, < 6)
+      redis-rack (>= 1, < 3)
+      redis-store (>= 1.1.0, < 1.4.0)
+    redis-activesupport (5.0.2)
+      activesupport (>= 3, < 6)
+      redis-store (~> 1.3.0)
+    redis-rack (2.0.2)
+      rack (>= 1.5, < 3)
+      redis-store (>= 1.2, < 1.4)
+    redis-rails (5.0.2)
+      redis-actionpack (>= 5.0, < 6)
+      redis-activesupport (>= 5.0, < 6)
+      redis-store (>= 1.2, < 2)
+    redis-store (1.3.0)
+      redis (>= 2.2)
     rest-client (1.6.8)
       mime-types (~> 1.16)
       rdoc (>= 2.4.2)
@@ -252,7 +267,6 @@ DEPENDENCIES
   byebug
   coffee-rails
   compass-rails
-  dalli
   database_cleaner
   diff-lcs
   dotenv-rails
@@ -265,7 +279,6 @@ DEPENDENCIES
   jquery-rails
   json
   launchy
-  memcachier
   netrc
   nokogiri
   octokit
@@ -275,6 +288,7 @@ DEPENDENCIES
   rails-perftest
   rails_12factor
   redcarpet
+  redis-rails
   rspec-rails
   ruby-prof
   rubyzip
@@ -293,4 +307,4 @@ RUBY VERSION
    ruby 2.1.8p440
 
 BUNDLED WITH
-   1.13.6
+   1.14.6

config/environments/production.rb

@@ -53,7 +53,7 @@ Rails.application.configure do
 
   # Use a different cache store in production.
   # config.cache_store = :mem_cache_store
-  config.cache_store = :dalli_store
+  config.cache_store = :redis_store, ENV['REDIS_URL']
 
   # Enable serving of images, stylesheets, and JavaScripts from an asset server.
   # config.action_controller.asset_host = "http://assets.example.com"