hakyll check: return exit code of 0 on success
hakyll check: return exit code of 0 on success

The old test returns an exit code of 1 whenever the number of
errors is >= 0, which should always be the case. The fix replaces
this with a test whether the number of errors is strictly > 0.

oldmanmike/hakyll,Minoru/hakyll,d12frosted/hakyll,Javran/hakyll,beni55/hakyll