[chore] Update to support log4js version 2.

### Expected behaviour
Works with  modern "log4js"
### Actual behaviour
Fails with 2.3.9  because setGlobalLogLevel is no longer part of the log4js API
### Environment Details

- Karma version 1.7.1
- Relevant part of your `karma.config.js` file
Not
### Steps to reproduce the behaviour

1. Update package.json to use log4js "^2.3.9"
2. 
3.
