Upgrade to 1.0.9

This upgrades the task to the latest stable upstream version [1.0.9](https://github.com/ronaldlokers/grunt-casperjs).

I have also included way to pass the ```ENVIRONMENT``` variable to the spawned child process, this is to make this kind of pattern easier:

- Set env variable in [Gruntfile.js](https://github.com/guardian/frontend/blob/fronts-admin-integration-tests/Gruntfile.js#L84)
- Set host in a shared include for all test suites [example](https://github.com/guardian/frontend/blob/fronts-admin-integration-tests/integration-tests/casper/tests/shared.js#L3)

Happy to discuss implications for both teams that use this in person.