Update dependency qunit to v2.9.1

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change	References
qunit	devDependencies	minor	2.8.0 -> 2.9.1	homepage, source

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Release Notes

qunitjs/qunit

### [`v2.9.1`](https://togithub.com/qunitjs/qunit/blob/master/History.md#​291--2019-01-07) [Compare Source](https://togithub.com/qunitjs/qunit/compare/2.9.0...2.9.1) ================== - Build: Fix (and add tests) missing required files in 2.9.0. ([#​1368](https://togithub.com/qunitjs/qunit/issues/1368)) - Build: Set "root: true" in eslintrc ### [`v2.9.0`](https://togithub.com/qunitjs/qunit/blob/master/History.md#​290--2019-01-06) [Compare Source](https://togithub.com/qunitjs/qunit/compare/2.8.0...2.9.0) ================== - Assert: Report RegExp/Error as strings from `rejects()`/`throws()` ([#​1333](https://togithub.com/qunitjs/qunit/issues/1333)) - Build: Add macOS and Windows to the Travis CI test matrix - Build: Update engine requirement package.json to Node 6 - CLI: Reduce size of the dependencies tree ([#​1342](https://togithub.com/qunitjs/qunit/issues/1342)) - CLI: Re-implement run.watch() with 'node-watch' instead of 'sane' ([#​1342](https://togithub.com/qunitjs/qunit/issues/1342)) - HTML Reporter: Fix an unescaped details.source ([#​1341](https://togithub.com/qunitjs/qunit/issues/1341))

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