Ensure urls use ascii encoding

As of Ruby 2.0.0, the default encoding is UTF-8. This will cause the
GoogleSafeBrowsing::Canonicalize unit tests provided by Google to fail
due to an "invalid byte sequence in UTF-8". Forcing the URLs to be
encoded in ASCII-8BIT (binary) first resolves the issue.
Merge pull request #5 from bethcrb/canonicalize_urls

Ensure URLs use ASCII encoding