Fix class name in sample code

[ursm]

Sprockets::Exporters::Zlip does not seem to exist.

[p8]

This makes sense to me as the register_exporter sample code uses ZlibExporter as well:

sprockets/lib/sprockets/exporting.rb

Line 15 in 8a20e9a

# register_exporter '*/*', Sprockets::Exporters::ZlibExporter

I don't think we need to add documentation changes to the CHANGELOG.

[ursm]

I don't think we need to add documentation changes to the CHANGELOG.

Got it, I deleted that commit.

[p8]

Thanks @ursm !