upgrade grunt-saucelabs to ~8.1.0

update shrinkwrap too
retry each test up to 3 times in the event of timeout

Big thanks to @gvas for https://github.com/axemclion/grunt-saucelabs/pull/136 ! <3
Merge pull request #13918 from twbs/sauce-with-retries

Enable retrying of timed-out Sauce tests