Fix HTML reporter regression causing duplicate error output (#2112)
Fix HTML reporter regression causing duplicate error output (#2112)

Fixes #2083.
nightwatchjs/mocha-nightwatch,Hacker0x01/mocha,menelaos/mocha-solarized,rlugojr/mocha,JohnnyEstilles/mocha,adamgruber/mocha,sul4bh/mocha,Khan/mocha,beatfactor/mocha,santiagoaguiar/mocha,rlugojr/mocha,hoverduck/mocha,boneskull/mocha,rlugojr/mocha,apkiernan/mocha,villesau/mocha,Hacker0x01/mocha,villesau/mocha,santiagoaguiar/mocha,sul4bh/mocha,hoverduck/mocha,hoverduck/mocha,Khan/mocha,hoverduck/mocha,beatfactor/mocha,mochajs/mocha,outsideris/mocha,boneskull/mocha,beatfactor/mocha,JohnnyEstilles/mocha,mochajs/mocha,menelaos/mocha-solarized,Khan/mocha,sul4bh/mocha,menelaos/mocha-solarized,villesau/mocha,apkiernan/mocha,nightwatchjs/mocha-nightwatch,apkiernan/mocha,adamgruber/mocha,Hacker0x01/mocha,igwejk/mocha,boneskull/mocha,santiagoaguiar/mocha,nightwatchjs/mocha-nightwatch,mochajs/mocha,igwejk/mocha,outsideris/mocha,JohnnyEstilles/mocha,adamgruber/mocha