/31 network is still incorrect

[realvitya]

Cygwin ~ $ ic 1.1.1.1/31
first host: 1.1.1.1/31
last host.: 1.1.1.2

The bug report for this initially:#17 The fix is not correct as seen above.
This may be a fix for the above bug:

def host_first(self):
    if (self.version() == 4 and self.mask > 30) or \
            (self.version() == 6 and self.mask > 126):
         -return self
         +return self.network()
...
def host_last(self):
    """Last available host in this subnet."""
    if (self.version() == 4 and self.mask == 32) or \
    ...
    elif (self.version() == 4 and self.mask == 31) or \
            (self.version() == 6 and self.mask == 127):
        -return IP(int(self) + 1, version=self.version())
        +return IP(int(self.network()) + 1, version=self.version())