Fixed HDF5 key for log10_specific_ionising_luminosity

[WillJRoper]

Q changes clashed in the cloudy input script.

Issue Type

• Bug

Checklist

• [x] I have read the [CONTRIBUTING.md]()
• [x] I have added docstrings to all methods
• [x] I have added sufficient comments to all lines
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no pep8 errors
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

[sophie-newman]

I am confused - why not log10_specific_ionising_lum as that's what we changed it to everywhere else?