Remove pipes module on versions > 3.3.

[elementalvoid]

The pipes module is deprecated as of 3.11 and is set to be removed in 3.13.

The shlex module introduced a quote function in 3.3 and the pipes module adopted it at the same time.

I performed the import in such a way as to continue to use the pipes.quote when it wasn't just a wrapper around shlex.quote. (Working under the assumption that you'd like to keep support for older versions.)

I also added newer Python versions to the PyPi classifiers and to the Travis config.

Let me know if there's anything you'd like to adjust (you also have edit permissions on the PR ¯\_(ツ)_/¯).

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I recognize this is similar to https://github.com/xolox/python-executor/pull/21. The main difference is that this change supports all Python versions.