Bugfix in composer.json

Tonight I tried to switch the Packagist entry for phpInsight so it points to your main phpInsight repo instead of my fork. But in the process I realized the version of composer.json that was in my earlier pull request had a typo that prevents Packagist (or any JSON parser) from being able to parse it.  How embarrassing. I fixed this many days ago, but I forgot to submit a new pull request. :-( Anyway, here's the fixed version.

Thanks!
-Curtis