travis: add some Ubuntu dependencies/correct gem command
travis: add some Ubuntu dependencies/correct gem command

Signed-off-by: George K. Thiruvathukal <97f75e7847f9d781491c82d5a21e2f28eba950b0@cs.luc.edu>

gkthiruvathukal/thiruvathukal.com,gkthiruvathukal/thiruvathukal.com