Fix Karma sinon-chai version issues

Previously, we were using the karma-sinon-chai package to
provide sinon-chai to karma.  This used an older version of
sinon-chai, and looks to be no longer maintained (it's been
a month since sinon-chai was updated).  A new package,
karma-sinon-chai-latest, is now used.  This package uses the
latest version of sinon-chai and sinon, just like karma-chai
uses the latest version of chai.