title: error with netlify cms deployment says Bundler v2 needed but bundler v2 was used
body: <p>When trying to deploy a jekyll site stored on github to netlify cms the build process throws this error</p>
  
  <pre><code>10:54:13 AM: Using ruby version 2.3.6
  10:54:13 AM: Using PHP version 5.6
  10:54:13 AM: Started restoring cached ruby gems
  10:54:13 AM: Finished restoring cached ruby gems
  10:54:13 AM: Installing gem bundle
  10:54:13 AM: You must use Bundler 2 or greater with this lockfile.
  10:54:13 AM: Error during gem install
  10:54:13 AM: failed during stage 'building site': Build script returned non-zero exit code: 1
  10:54:13 AM: Error running command: Build script returned non-zero exit code: 1
  10:54:13 AM: Failing build: Failed to build site
  </code></pre>
  
  <p>Note how it says bundler 2 or greater should be used.</p>
  
  <p>In the GemFile.lock</p>
  
  <p>at the end it shows....</p>
  
  <pre><code>BUNDLED WITH
  2.0.1
  </code></pre>
  
  <p>Anyone any idea what is going on or how I can investigate/resolve this build error given that the site appears to meet the requirement already.</p>
  
  <p>Or is it telling me that I need to configure the netlify build process to use Bundler 2? If so is this possible?</p>