Ugrade lolex to v5 and don't detect globals

[mantoni]

This integrates the latest lolex and introduces the --no-detect-globals flag for browserify bundles and tests.

There is also a solution for running the tests using JSDOM on node and the actual DOM in headless chrome.

Note that we used to browserify jsdom, jsdom-global and @sinonjs/text-encoding. Putting those on the ignore list speeds up test runs significantly.

The global-hack.js thing is needed due to the circular dependencies that we have. Once Sinon includes all the latest, this can be removed.

[codecov]

Codecov Report

Merging #108 into master will decrease coverage by 0.28%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #108      +/-   ##
==========================================
- Coverage   90.86%   90.57%   -0.29%     
==========================================
  Files          12       13       +1     
  Lines         602      605       +3     
==========================================
+ Hits          547      548       +1     
- Misses         55       57       +2

Flag	Coverage Δ
#unit	90.57% <66.66%> (-0.29%)	⬇️

Impacted Files	Coverage Δ
test/global-hack.js	0% <0%> (ø)
lib/fake-xhr/index.js	86.95% <100%> (+0.03%)	⬆️

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[mantoni]

Hm. We don't run test:headless on CI yet 🤔

[mroderick]

That should be an easy fix