title: Selenium-webdriver zip issue
body: <p>Yesterday my rspec +selenium was running fine. Today when i ran tests i got: </p>
  
  <pre><code> Failure/Error: Unable to find matching line from backtrace
   NameError:
     uninitialized constant Zip::File
   # /home/mygemsetpathd/gems/selenium-webdriver-2.37.0/lib/selenium/webdriver/common/zipper.rb:21:in `unzip'
  </code></pre>
  
  <p>Then i updates selenium-webdriver to 2.39.0 but error is the same. 
  I have gem 'zip' and gem 'rubyzip',  "~> 1.0", require: 'zip' in my Gemfile. </p>
  
  <p>Thanks for any suggestions.</p>