Added Travis configuration
Added Travis configuration

This will test anything pushed to github against AG 6.4.0, 6.3.0 and 6.2.3.

The 6.4.0 tests are run in all supported versions of Python (2.7 - 3.6),
all other tests run only on Python 3.6.

Change-Id: Id5fbd8fc1686ba21046c5fbce8080ad2730fc0b4
Reviewed-on: https://gerrit.franz.com:9080/9480
Reviewed-by: Tadeusz Sznuk <4402abb98f9559cbfb6d73029f928227b498069b@franz.com>
Tested-by: Hudson <dfb64870173313a9a7b56f814c8e3b33e268497a@franz.com>
Reviewed-by: Hudson <dfb64870173313a9a7b56f814c8e3b33e268497a@franz.com>
Reviewed-by: Ahmon Dancy <8f7d8ce2c6797410ae95fecd4c30801ee9f760ac@franz.com>

franzinc/agraph-python,franzinc/agraph-python,franzinc/agraph-python,franzinc/agraph-python