JOSS paper: pyvisa reference

[MatthieuDartiailh]

The usual syntax for PyVISA is this one not pyVISA and PyVISA-py not pyVISApy. The paper use the right casing for the reference to PyVISA-py but not in other occurrences nor for PyVISA

Also note that both PyVISA and PyVISA-py have documentation hosted on readthedocs but the paper currently use readthedocs for PyVISA and github for PyVISA-py

openjournals/joss-reviews#4752

[OHildreth]

Thank you. We have fixed the spelling on all PyVISA and PyVISA-py. Additionally, we have updated the citation for PyVISA-py to reference the readthedocs.