update CHANGELOG for v3.1.1 [ci skip]
update CHANGELOG for v3.1.1 [ci skip]

nightwatchjs/mocha-nightwatch,sul4bh/mocha,rlugojr/mocha,adamgruber/mocha,menelaos/mocha-solarized,villesau/mocha,rlugojr/mocha,apkiernan/mocha,rlugojr/mocha,outsideris/mocha,JohnnyEstilles/mocha,mochajs/mocha,JohnnyEstilles/mocha,outsideris/mocha,boneskull/mocha,hoverduck/mocha,JohnnyEstilles/mocha,hoverduck/mocha,beatfactor/mocha,mochajs/mocha,igwejk/mocha,villesau/mocha,boneskull/mocha,sul4bh/mocha,boneskull/mocha,adamgruber/mocha,villesau/mocha,hoverduck/mocha,beatfactor/mocha,nightwatchjs/mocha-nightwatch,menelaos/mocha-solarized,apkiernan/mocha,mochajs/mocha,nightwatchjs/mocha-nightwatch,beatfactor/mocha,igwejk/mocha,sul4bh/mocha,adamgruber/mocha,menelaos/mocha-solarized,hoverduck/mocha,apkiernan/mocha