somebody forgot to update the gemfile.lock - this will help.

Gemfile

@@ -15,7 +15,7 @@ gem 'foreman'
 group :test do
   gem 'rspec'
   gem 'capybara'
-  gem 'selenium'
+  gem 'selenium-webdriver'
   gem 'rack-test'
   gem 'simplecov'
   gem 'curb'

Gemfile.lock

@@ -8,9 +8,8 @@ GEM
       rack (>= 1.0.0)
       rack-test (>= 0.5.4)
       xpath (~> 2.0)
-    capybara-webkit (1.0.0)
-      capybara (~> 2.0, >= 2.0.2)
-      json
+    childprocess (0.3.9)
+      ffi (~> 1.0, >= 1.0.11)
     cookiejar (0.3.0)
     curb (0.8.3)
     daemons (1.1.9)
@@ -34,13 +33,13 @@ GEM
       yajl-ruby (>= 1.0.0)
     faye-websocket (0.4.7)
       eventmachine (>= 0.12.0)
+    ffi (1.9.0)
     foreman (0.63.0)
       dotenv (>= 0.7)
       thor (>= 0.13.6)
     haml (4.0.3)
       tilt
     http_parser.rb (0.5.3)
-    json (1.8.0)
     mime-types (1.23)
     mini_portile (0.5.1)
     multi_json (1.7.8)
@@ -60,6 +59,12 @@ GEM
     rspec-expectations (2.14.0)
       diff-lcs (>= 1.1.3, < 2.0)
     rspec-mocks (2.14.2)
+    rubyzip (0.9.9)
+    selenium-webdriver (2.33.0)
+      childprocess (>= 0.2.5)
+      multi_json (~> 1.0)
+      rubyzip
+      websocket (~> 1.0.4)
     simplecov (0.7.1)
       multi_json (~> 1.0)
       simplecov-html (~> 0.7.1)
@@ -74,6 +79,7 @@ GEM
       rack (>= 1.0.0)
     thor (0.18.1)
     tilt (1.4.1)
+    websocket (1.0.7)
     xpath (2.0.0)
       nokogiri (~> 1.3)
     yajl-ruby (1.1.0)
@@ -83,14 +89,14 @@ PLATFORMS
 
 DEPENDENCIES
   capybara
-  capybara-webkit
   curb
   faye
   foreman
   haml
   rack-test
   rake
   rspec
+  selenium-webdriver
   simplecov
   sinatra
   thin

sinatra/spec/spec_helper.rb

@@ -1,6 +1,5 @@
 require 'rspec'
 require 'capybara/rspec'
-require 'capybara/webkit'
 require 'simplecov'
 SimpleCov.start
 require_relative '../rat_pack_server'