Log Message:
py-cares: updated to 2.4.0

Version 2.4.0
- misc: fix building wheels for unavailable Python versions
- test: skip getaddrinfo6 test on Travis
- doc: add FreeBSD building instructions
- build: fix MinGW build
- ci, misc: add support for CPython 3.7
- ci: run on latest PyPy versions on TravisCI
- examples: extra examples
- ci: fix AppVeyor build
- test: fix TXT test
- core: fix repr for PTR results