remove remaining import of `github.com/go-kit/kit/log` in apache_exporter.go

[Lusitaniae]

Thank you both, new Debian package on its way.

One tiny nit: there is one remaining import of github.com/go-kit/kit/log in apache_exporter.go which could be replaced with github.com/go-kit/log. This is not a big deal though, and does not justify a new tag.

Originally posted by @dswarbrick in #120 (comment)