所有测试通过时，我看到以下错误
ERROR: invocation failed (exit code 1), logfile:
/home/travis/build/username/projectA/.tox/py34/log/py34-2.log
ERROR: actionid: py34
...
___________________________________ summary ____________________________________
ERROR: py34: InvocationError: /home/travis/build/username/projectA/.tox/py34/bin/pip install /home/travis/build/username/projectA/.tox/dist/projectA-0.0.0.zip (see /home/travis/build/username/projectA/.tox/py34/log/py34-2.log)
...
----------- coverage: platform linux, python 3.4.6-final-0 -----------
Coverage HTML written to dir htmlcov
========================== 254 passed in 2.63 seconds ==========================
对于py35和py36不会发生这种情况。知道为什么吗？