fix CI

Don't use node install -g on travis, dependencies installed that way get
shadowed by older versions in directories that occur earlier in $PATH.

In this case, bower 0.10.0 was getting npm install -g'd but 0.9.2 was being
used, which did not yet support installing a dependency by git revision.

Also use "grunt test" rather than calling karma directly so more of the build
and developer workflow is actually tested, and switch karma to use phantomjs
for headless browser testing (comes with Travis CI, but karma's default
browser, Chrome, does not).