[python-control-developers] [python-control/python-control] 06aaec: Stop testing Python 2.7, 3.5 and scipy 0.19

[Ben G. <no...@gi...>]

  Branch: refs/heads/drop-old-py-scipy
  Home:   https://github.com/python-control/python-control
  Commit: 06aaec32e30c541f0b4e4749a0a7ab0a3f8a1379
      https://github.com/python-control/python-control/commit/06aaec32e30c541f0b4e4749a0a7ab0a3f8a1379
  Author: Ben Greiner <co...@bn...>
  Date:   2020-12-29 (Tue, 29 Dec 2020)

  Changed paths:
    M .travis.yml

  Log Message:
  -----------
  Stop testing Python 2.7, 3.5 and scipy 0.19

merging #447, which did not fail in the PR tests, started to fail master after the merge, because `cont2discrete(..., 'impulse')` fails.

Following NEP 29 we could even drop 3.6. But that is still active in distributions like openSUSE Leap 15.x, so I would like to keep that.