Fix installation procedure

[ibusko]

The procedures in the readthedocs installation page fail to install specviz.

When installing from sources, it finishes the installation procedure, but then the app itself crashes with
ModuleNotFoundError: No module named 'specutils.core'

When pip-installing, an error from numpy (apparently) crashes the install itself:
RuntimeError: implement_array_function method already has a docstring

[pllim]

Same reported on Astropy mailing list: https://mail.python.org/pipermail/astropy/2019-September/004582.html

Can one of the maintainers please answer over there? Thanks.

[nmearl]

@ibusko how are you installing specviz? You may wish to check your package versions as well:

python -c "import specviz; print(specviz.__version__)"
python -c "import specutils; print(specutils.__version__)"

SpecViz should return version 0.7.0, and specutils should return version 0.5.2.

[ibusko]

@nmearl I just re-installed everything from scratch, following the readthedocs recipe. I had to do a conda update. And now it works. And the reported versions are correct.

So maybe the older conda version was the culprit? Interestingly, I hadn't have the alert 'Please update conda by running....' even recently, when creating conda environments on this machine. But the problem seems to have been fixed by itself. I will close this issue.

[ibusko]

I will take care of the issue in the astropy mailing list as well.

[pllim]

Thanks!