What is the minimum numpy required?

[mhvk]

In testing in our scintillometry package, the runs with numpy at 1.14 stopped working with #549 by @aarchiba - I think this is not a problem and we needed to update our minimum version of numpy anyway, but I could't find what PINT's minimum numpy is (or, rather, IIRC, requirements.txt gives 1.11 or so and requirements_dev.txt doesn't list it).

[mhvk]

Just to be a bit clearer: the use of np.nditer as a context manager is only possible since numpy >=1.15. That does seem a reasonable minimum version, but it would be good to be explicit about this (and have a travis run that tests with the minimum supported version!).

[paulray]

Anyone know how to make a travis run that sets all the packages at the minimum supported version?

[mhvk]

@paulray - over at astropy, we've just switched over to setting up environments with tox (which I see PINT has started to use as well), and in tox.ini, there's:

https://github.com/astropy/astropy/blob/424b3fb21f8cdf61db7fccb16ceee4c8bc99a80e/tox.ini#L49-L53

which then gets used in .travis.yml as:

https://github.com/astropy/astropy/blob/424b3fb21f8cdf61db7fccb16ceee4c8bc99a80e/.travis.yml#L79-L88