minor config change
minor config change

actually to test whether i can get saucelabs to stop failing in parallel
by changing the travis option to sequential

mtraynham/dc.js,ruhley/dc.js,becompany/dc.js,r4j4h/dc.js,r4j4h/dc.js,ruhley/dc.js,dc-js/dc.js,ruhley/dc.js,maackle/dc.js,mtraynham/dc.js,ruhley/dc.js,Hauenstein/dc.js,dc-js/dc.js,ruhley/dc.js,TheDataShed/dc.js,Hauenstein/dc.js,aaronhoffman/dc.js,r4j4h/dc.js,mtraynham/dc.js,becompany/dc.js,becompany/dc.js,TheDataShed/dc.js,TheDataShed/dc.js,aaronhoffman/dc.js,dc-js/dc.js,aaronhoffman/dc.js,maackle/dc.js,Hauenstein/dc.js,r4j4h/dc.js,r4j4h/dc.js,maackle/dc.js,maackle/dc.js,TheDataShed/dc.js,mtraynham/dc.js,dc-js/dc.js,aaronhoffman/dc.js,maackle/dc.js,Hauenstein/dc.js,dc-js/dc.js,TheDataShed/dc.js,mtraynham/dc.js,Hauenstein/dc.js,aaronhoffman/dc.js