chore(package): update sinon to version 2.3.1 (#955)
chore(package): update sinon to version 2.3.1 (#955)

Closes #952
mozilla/web-ext,rpl/web-ext,mozilla/web-ext,shubheksha/web-ext,rpl/web-ext,kumar303/web-ext,shubheksha/web-ext,kumar303/web-ext