title: jekyll 3.1.6 | Error: uninitialized constant Jekyll::Filters::URLFilters
body: <p>Hello Jekyll support users</p>
  
  <p>I need serve this repository on Jekyll, but I has this error on Ubuntu 17.04 Terminal</p>
  
  <pre><code>geraldo@geraldo-Dell-System-XPS-L322X:~/Documentos/activate.mozilla.community$ bundle exec jekyll serve --config ./_config-dev.yml
  /var/lib/gems/2.3.0/gems/jekyll-3.4.3/lib/jekyll/drops/document_drop.rb:8: warning: already initialized constant Jekyll::Drops::DocumentDrop::NESTED_OBJECT_FIELD_BLACKLIST
  /usr/lib/ruby/vendor_ruby/jekyll/drops/document_drop.rb:8: warning: previous definition of NESTED_OBJECT_FIELD_BLACKLIST was here
  /var/lib/gems/2.3.0/gems/jekyll-3.4.3/lib/jekyll/drops/drop.rb:8: warning: already initialized constant Jekyll::Drops::Drop::NON_CONTENT_METHODS
  /usr/lib/ruby/vendor_ruby/jekyll/drops/drop.rb:8: warning: previous definition of NON_CONTENT_METHODS was here
  Configuration file: ./_config-dev.yml
  Configuration file: ./_config-dev.yml
  jekyll 3.1.6 | Error:  uninitialized constant Jekyll::Filters::URLFilters
  </code></pre>
  
  <p>Anyone here to help me?</p>