Fix reduction order in Nock spec

The way one is supposed to use the Nock spec is by repeatedly going
through the reduction rules from top to bottom, and applying the first
rule that matches. Some rules appeared to be in the wrong order: a more
general rule was above a more specific rule, making the latter
unreachable.
Merge pull request #14 from ab9/fix_nock_reduction_order

Fix reduction order in Nock spec