hostname tests are skipped due to incorrect type of `canonname`

[dealbreaker973]

Hi, when I try to run the pytest, I noticed that hostname-related tests are skipped even when the nameserver supports the AI_CANONNAME flag. This was possibly due to the incorrect type of the expected result when testing for the AI_CANONNAME flag: https://github.com/JordanMilne/Advocate/blob/master/test/test_advocate.py#L55

The cannonname returned by socket.getaddrinfo is a string now. ref: https://docs.python.org/3/library/socket.html#socket.getaddrinfo

When running hostname-related tests, HostnameTests.test_idn failed:

======================================= FAILURES =======================================
________________________________ HostnameTests.test_idn ________________________________
self = <test.test_advocate.HostnameTests testMethod=test_idn>

    def test_idn(self):
        # test some basic globs
>       self.assertFalse(self._is_hostname_allowed(
            u"中国.example.org",
            fake_lookup=True,
            hostname_blacklist={"*.org"}
        ))

test/test_advocate.py:359:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
test/test_advocate.py:350: in _is_hostname_allowed
    if validator.is_addrinfo_allowed(res):
advocate/addrvalidator.py:58: in wrapper
    return func(self, *args, **kwargs)
advocate/addrvalidator.py:319: in is_addrinfo_allowed
    if not self.is_hostname_allowed(canonname):
advocate/addrvalidator.py:259: in is_hostname_allowed
    if self._hostname_matches_pattern(hostname, pattern):
advocate/addrvalidator.py:221: in _hostname_matches_pattern
    hostname = canonicalize_hostname(hostname)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

hostname = b'xn--fiqs8s.example.org'

    def canonicalize_hostname(hostname):
        """Lowercase and punycodify a hostname"""
        # We do the lowercasing after IDNA encoding because we only want to
        # lowercase the *ASCII* chars.
        # TODO: The differences between IDNA2003 and IDNA2008 might be relevant
        # to us, but both specs are damn confusing.
>       return str(hostname.encode("idna").lower(), 'utf-8')
E       AttributeError: 'bytes' object has no attribute 'encode'

advocate/addrvalidator.py:23: AttributeError
=============================== short test summary info ================================
FAILED test/test_advocate.py::HostnameTests::test_idn - AttributeError: 'bytes' object has no attribute 'encode'

Similar to the cannoname bug, this is also introduced by feeding bytes as the cannoname in the _is_hostname_allowed function: https://github.com/JordanMilne/Advocate/blob/master/test/test_advocate.py#L346

I can make a PR later for a quick fix of the issues mentioned above