title: Bundle using old version of jekyll
body: <p>I am trying to preview a site I have built in the past, using jekyll. Since then, I believe there have been updates to jekyll, and I now use <code>zsh</code> on MacOS 10.15.2. I'm having trouble now running a preview because it seems <code>bundle</code> keeps using an old version of <code>jekyll</code>. </p>
  
  <p>When I run <code>bundle exec jekyll server --unpublished</code> I receive this error:</p>
  
  <pre><code>(base) ➜  angoodkind.github.io git:(master) ✗ bundle exec jekyll server --unpublished
  Configuration file: /Users/adamg/Dropbox/Website/github_io/angoodkind.github.io/_config.yml
  NOTE: Inheriting Faraday::Error::ClientError is deprecated; use Faraday::ClientError instead. It will be removed in or after version 1.0
  Faraday::Error::ClientError.inherited called from /Users/adamg/Dropbox/Website/github_io/angoodkind.github.io/vendor/cache/ruby/2.6.0/gems/octokit-4.14.0/lib/octokit/middleware/follow_redirects.rb:14.
              Source: /Users/adamg/Dropbox/Website/github_io/angoodkind.github.io
         Destination: /Users/adamg/Dropbox/Website/github_io/angoodkind.github.io/_site
   Incremental build: disabled. Enable with --incremental
        Generating...
  Error reading file /Users/adamg/Dropbox/Website/github_io/angoodkind.github.io/blog/index.html: (&lt;unknown&gt;): did not find expected key while parsing a block mapping at line 7 column 5
               Error: could not read file /Users/adamg/Dropbox/Website/github_io/angoodkind.github.io/vendor/cache/ruby/2.6.0/gems/jekyll-3.5.2/lib/site_template/_posts/0000-00-00-welcome-to-jekyll.markdown.erb: Invalid date '&lt;%= Time.now.strftime('%Y-%m-%d %H:%M:%S %z') %&gt;': Document 'vendor/cache/ruby/2.6.0/gems/jekyll-3.5.2/lib/site_template/_posts/0000-00-00-welcome-to-jekyll.markdown.erb' does not have a valid date in the YAML front matter.
               ERROR: YOUR SITE COULD NOT BE BUILT:
                      ------------------------------------
                      Invalid date '&lt;%= Time.now.strftime('%Y-%m-%d %H:%M:%S %z') %&gt;': Document 'vendor/cache/ruby/2.6.0/gems/jekyll-3.5.2/lib/site_template/_posts/0000-00-00-welcome-to-jekyll.markdown.erb' does not have a valid date in the YAML front matter.
  </code></pre>
  
  <p>However, the system should be using jekyll 4.0.0, which was recently installed. Why is it using jekyll 3.5.2?</p>