title: miniconda and Travis, what does hash -r do?
body: <p>In <a href="https://docs.conda.io/projects/conda/en/latest/user-guide/tasks/use-conda-with-travis-ci.html" rel="nofollow noreferrer">Conda's manual for Travis integration</a>, what does <code>hash -r</code> do and is it necessary?</p>