have VCR allow Webmock 1.12
don't pass an Addressable::URI to Net::HTTP

It chokes. References #272
normalize response encoding for Ruby 2.0 in test

Ruby 2.0 reads the HTTP response body as UTF-8 by default, where older
Rubies interpreted it as US-ASCII and thus VCR serialized it that way.
For the purpose of this test, force the response body to US-ASCII
encoding so that the outcome of serialization is normalized between
different Ruby versions.
don't tolerate Ruby 2.0 failures anymore