chore(package): update mz to version 2.4.0
chore(package): update mz to version 2.4.0

http://greenkeeper.io/
kumar303/web-ext,rpl/web-ext,rpl/web-ext,mozilla/web-ext,shubheksha/web-ext,mozilla/web-ext,kumar303/web-ext,shubheksha/web-ext