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.