Also, run `grunt npmcopy` to sync the "external" directory with dependencies
from package.json. For example, the Sinon library version didn't match.
Ref gh-4234
Closes gh-4297
All deps were updated except:
* jsdom - tests using a Symbol polyfill are hacky and break with newer jsdom;
we need to re-do them properly first
* qunitjs - versions 1.19.0 & 1.20.0 introduce race conditions to the tests,
making the fail randomly
Those two packages will be updated once issues related to them get resolved.
Fixes gh-2877
