JSON::Ext::Generator is not a module

gistfile1.txt

# bin/arachni http://demo.testfire.net
/root/tools/arachni-2.0dev-1.0dev/system/usr/lib/ruby/2.3.0/json/ext.rb:15:in `require': JSON::Ext::Generator is not a module (Class) (TypeError)
        from /root/tools/arachni-2.0dev-1.0dev/system/usr/lib/ruby/2.3.0/json/ext.rb:15:in `<module:Ext>'
        from /root/tools/arachni-2.0dev-1.0dev/system/usr/lib/ruby/2.3.0/json/ext.rb:13:in `<module:JSON>'
        from /root/tools/arachni-2.0dev-1.0dev/system/usr/lib/ruby/2.3.0/json/ext.rb:10:in `<top (required)>'
        from /root/tools/arachni-2.0dev-1.0dev/system/usr/lib/ruby/2.3.0/json.rb:59:in `require'
        from /root/tools/arachni-2.0dev-1.0dev/system/usr/lib/ruby/2.3.0/json.rb:59:in `<module:JSON>'
        from /root/tools/arachni-2.0dev-1.0dev/system/usr/lib/ruby/2.3.0/json.rb:55:in `<top (required)>'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/gems/selenium-webdriver-2.53.0/lib/selenium/webdriver.rb:24:in `require'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/gems/selenium-webdriver-2.53.0/lib/selenium/webdriver.rb:24:in `<top (required)>'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/gems/selenium-webdriver-2.53.0/lib/selenium-webdriver.rb:20:in `require'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/gems/selenium-webdriver-2.53.0/lib/selenium-webdriver.rb:20:in `<top (required)>'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/gems/watir-webdriver-0.8.0/lib/watir-webdriver.rb:1:in `require'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/gems/watir-webdriver-0.8.0/lib/watir-webdriver.rb:1:in `<top (required)>'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/lib/arachni/browser.rb:10:in `require'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/lib/arachni/browser.rb:10:in `<top (required)>'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/lib/arachni/browser_cluster/worker.rb:12:in `require'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/lib/arachni/browser_cluster/worker.rb:12:in `<module:Arachni>'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/lib/arachni/browser_cluster/worker.rb:10:in `<top (required)>'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/lib/arachni/browser_cluster.rb:42:in `require'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/lib/arachni/browser_cluster.rb:42:in `<class:BrowserCluster>'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/lib/arachni/browser_cluster.rb:14:in `<module:Arachni>'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/lib/arachni/browser_cluster.rb:9:in `<top (required)>'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/lib/arachni/framework.rb:39:in `require'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/lib/arachni/framework.rb:39:in `<module:Arachni>'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/lib/arachni/framework.rb:17:in `<top (required)>'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/lib/arachni.rb:103:in `require_relative'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/lib/arachni.rb:103:in `<top (required)>'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/ui/cli/framework.rb:9:in `require_relative'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/ui/cli/framework.rb:9:in `<top (required)>'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/bin/arachni:10:in `require_relative'
        from /root/tools/arachni-2.0dev-1.0dev/system/gems/bundler/gems/arachni-77035451dd8d/bin/arachni:10:in `<top (required)>'
        from /root/tools/arachni-2.0dev-1.0dev/bin/../system/arachni-ui-web/bin/arachni:17:in `load'
        from /root/tools/arachni-2.0dev-1.0dev/bin/../system/arachni-ui-web/bin/arachni:17:in `<main>'