to avoid the exit status 1
() does not work in travis section tags
do not use xvfb (yet), since it might cause hang
hot.deck and pkgmaker are time-consuming as well
yihui updated branch pkg/knitr Mon Oct  6 01:37:39 CDT 2014
yihui updated branch pkg/knitr Mon Oct  6 13:00:30 CDT 2014
yihui updated branch pkg/knitr Tue Oct  7 11:27:40 CDT 2014