travis: run Karma with dots reporter

This looks better in the final report. The progress reporter we
accidentally used since 74995de18d gives a listing like this:

  SUCCESS (0 secs / 0.049 secs)
  SUCCESS (0 secs / 0.057 secs)
  SUCCESS (0 secs / 0.065 secs)
  SUCCESS (0 secs / 0.071 secs)

While the timings might be nice, they are less helpful when the test
name isn't printed.
karma: standardize on "key: value", not "key : value"