Update Travis config.
Update Travis config.

* remove `dist: trusty` since it's the default
* disable email notifications

m5o/bootstrap,nice-fungal/bootstrap,GerHobbelt/bootstrap,gijsbotje/bootstrap,gijsbotje/bootstrap,fschumann1211/bootstrap,stanwmusic/bootstrap,stanwmusic/bootstrap,kvlsrg/bootstrap,yuyokk/bootstrap,inway/bootstrap,tagliala/bootstrap,zalog/bootstrap,bardiharborow/bootstrap,bardiharborow/bootstrap,coliff/bootstrap,GerHobbelt/bootstrap,kvlsrg/bootstrap,gijsbotje/bootstrap,fschumann1211/bootstrap,peterblazejewicz/bootstrap,twbs/bootstrap,zalog/bootstrap,tjkohli/bootstrap,bardiharborow/bootstrap,yuyokk/bootstrap,twbs/bootstrap,coliff/bootstrap,GerHobbelt/bootstrap,kvlsrg/bootstrap,fschumann1211/bootstrap,yuyokk/bootstrap,zalog/bootstrap,stanwmusic/bootstrap,inway/bootstrap,peterblazejewicz/bootstrap,peterblazejewicz/bootstrap,yuyokk/bootstrap,gijsbotje/bootstrap,m5o/bootstrap,nice-fungal/bootstrap,tagliala/bootstrap,nice-fungal/bootstrap,tjkohli/bootstrap,inway/bootstrap,tagliala/bootstrap,stanwmusic/bootstrap,bardiharborow/bootstrap,fschumann1211/bootstrap