Update sidekiq, remove sinatra dependency

Gemfile

@@ -36,7 +36,6 @@ gem 'simple_form'
 gem 'will_paginate'
 gem 'rack-attack'
 gem 'sidekiq'
-gem 'sinatra', require: nil, git: 'https://github.com/sinatra/sinatra.git'
 
 gem 'react-rails'
 gem 'browserify-rails'

Gemfile.lock

@@ -1,15 +1,3 @@
-GIT
-  remote: https://github.com/sinatra/sinatra.git
-  revision: 1b0edc0aeaaf4839cadfcec1b21da86e6af1d4c0
-  specs:
-    rack-protection (2.0.0.beta2)
-      rack
-    sinatra (2.0.0.beta2)
-      mustermann (= 1.0.0.beta2)
-      rack (~> 2.0)
-      rack-protection (= 2.0.0.beta2)
-      tilt (~> 2.0)
-
 GEM
   remote: https://rubygems.org/
   specs:
@@ -177,7 +165,6 @@ GEM
     mini_portile2 (2.1.0)
     minitest (5.9.0)
     multi_json (1.12.1)
-    mustermann (1.0.0.beta2)
     nio4r (1.2.1)
     nokogiri (1.6.8)
       mini_portile2 (~> 2.1.0)
@@ -214,6 +201,8 @@ GEM
     rack (2.0.1)
     rack-attack (5.0.1)
       rack
+    rack-protection (1.5.3)
+      rack
     rack-test (0.6.3)
       rack (>= 1.0)
     rails (5.0.0.1)
@@ -306,9 +295,10 @@ GEM
       json (~> 1.7, >= 1.7.7)
       rdoc (~> 4.0)
     sexp_processor (4.7.0)
-    sidekiq (4.1.2)
+    sidekiq (4.2.1)
       concurrent-ruby (~> 1.0)
       connection_pool (~> 2.2, >= 2.2.0)
+      rack-protection (~> 1.5)
       redis (~> 3.2, >= 3.2.1)
     simple_form (3.2.1)
       actionpack (> 4, < 5.1)
@@ -402,7 +392,6 @@ DEPENDENCIES
   sidekiq
   simple_form
   simplecov
-  sinatra!
   therubyracer
   uglifier (>= 1.3.0)
   webmock