Update Karma dependency to resolve security issues

Resolves a subset of the security issues identified by `npm audit`.

Before:

    found 27 vulnerabilities (16 low, 1 moderate, 9 high, 1 critical)

(full audit: https://gist.github.com/wincent/96a0bae65e9a5b681c3103bb6a9c5471)

After:

    found 15 vulnerabilities (7 low, 1 moderate, 6 high, 1 critical)

(full audit: https://gist.github.com/wincent/c61df833b3855ea5efa1ae108e7c5006)

`npm run test` is clean after the update:

```
15 01 2019 14:06:26.772:INFO [karma]: Karma v1.4.0 server started at http://0.0.0.0:9876/
15 01 2019 14:06:26.773:INFO [launcher]: Launching browser Chrome with unlimited concurrency
15 01 2019 14:06:26.791:INFO [launcher]: Starting browser Chrome
15 01 2019 14:06:27.799:INFO [Chrome 71.0.3578 (Mac OS X 10.13.6)]: Connected on socket c-wYPd2u1z3iqI36AAAA with id 39092991
Chrome 71.0.3578 (Mac OS X 10.13.6): Executed 87 of 356 SUCCESS (0 secs / 0.405 secs)
Chrome 71.0.3578 (Mac OS X 10.13.6): Executed 92 of 356 (skipped 6) SUCCESS (0 secs / 0.433 secs)
Chrome 71.0.3578 (Mac OS X 10.13.6): Executed 103 of 356 (skipped 6) SUCCESS (0 secs / 0.552 secs)
Chrome 71.0.3578 (Mac OS X 10.13.6): Executed 111 of 356 (skipped 6) SUCCESS (0 secs / 0.859 secs)
Chrome 71.0.3578 (Mac OS X 10.13.6): Executed 119 of 356 (skipped 6) SUCCESS (0 secs / 1.163 secs)
Chrome 71.0.3578 (Mac OS X 10.13.6): Executed 121 of 356 (skipped 6) SUCCESS (0 secs / 1.164 secs)
Chrome 71.0.3578 (Mac OS X 10.13.6): Executed 174 of 356 (skipped 8) SUCCESS (0 secs / 1.37 secs)
ERROR: 'Warning: `value` prop on `%s` should not be null. Consider using an empty string to clear the component or `undefined` for uncontrolled components.%s', 'input', '
    in input
    in div
    in div
    in div
    in _class'
Chrome 71.0.3578 (Mac OS X 10.13.6): Executed 322 of 356 (skipped 14) SUCCESS (0 secs / 2.382 secs)
Chrome 71.0.3578 (Mac OS X 10.13.6): Executed 342 of 356 (skipped 14) SUCCESS (5.33 secs / 2.429 secs)
```

Related: https://issues.liferay.com/browse/IFI-405

Author: wincent