chore: add sinonjs dependency w/ alternative repo (#1690)
chore: add sinonjs dependency w/ alternative repo (#1690)

Repository github.com/blittle/sinon.js was deleted
And bower install fails
Workaround for Polymer/tools#3488
While Polymer/tools#3489 isn't merged and released
vaadin/components,vaadin/components,vaadin/components,vaadin/vaadin-grid,vaadin/vaadin-grid