Python 3.7 support

[idantene]

Heya.
After playing a bit with the library (well done!), I've found that, at least on Python 3.7 (which is now officially released), then pook.off() doesn't work.
Moreover, enable_network (with and without hosts) doesn't work. Without host there just seems to be no effect (still raises exception on unmatched requests), and with hosts it yells about incompatibility between a tuple and a list/string.

Would be happy to help fixing these if needed!

[h2non]

This should be fixed in latest release!