Update dependency karma to v4

[renovate-bot]

This PR contains the following updates:

Package	Type	Update	Change	References
karma	devDependencies	major	3.1.4 -> 4.0.0	homepage, source

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Release Notes

karma-runner/karma

v4.0.0

Compare Source

Bug Fixes

• client: fix issue with loaded on safari 10 (#​3252) (571191c), closes #​3198
• config: add test:unit npm script (#​3242) (02f071d)

Chores

• remove support for node 6 (#​3246) (8a83990), closes #​3151

BREAKING CHANGES

• Drop Support for Node 6, to make it possible to use async/await in karma codebase.

3.1.4 (2018-12-17)

Bug Fixes

• file-list: revert "do not preprocess up-to-date files" (#​3226) (#​3230) (bb022a7)
• improve error msg when bin is a directory (#​3231) (584dddc)
• restarted browsers not running tests (#​3233) (cc2eff2)

3.1.3 (2018-12-01)

Bug Fixes

• add missing dep flatted (#​3223) (655d4d2)

3.1.2 (2018-12-01)

Bug Fixes

• browser: report errors to console during singleRun=false (#​3209) (30ff73b), closes #​3131
• changelog: remove release which does not exist (#​3214) (4e87902)
• dep: Bump useragent to fix HeadlessChrome version (#​3201) (240209f), closes #​2762
• deps: upgrade sinon-chai 2.x -> 3.x (#​3207) (dc5f5de)
• file-list: do not preprocess up-to-date files (#​3196) (5334d1a), closes #​2829
• package: bump lodash version (#​3203) (d38f344), closes #​3177
• server: use flatted for json.stringify (#​3220) (fb05fb1), closes #​3215

Features

• docs: callout the key debug strategies. (#​3219) (2682bff)

3.1.1 (2018-10-23)

Bug Fixes

• config: move puppeteer from dependency to dev-dependency (#​3193) (f0d52ad), closes #​3191

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[rsimha]

/cc @estherkim @danielrozenberg @erwinmombay