Well there is a JSHint specific configuration for the [node/browser files](https://github.com/karma-runner/karma/blob/master/Gruntfile.coffee#L52-68). So there is two possibilities:
- export `JSHINT_NODE` and `JSHINT_BROWSER` into the appropriate file in the common config
- keep the situation as is: i.e. merge `JSHINT_NODE` and `JSHINT_BROWSER` into the common config using `deepmerge`