Use `#minus` instead of hypen `-` for luminosity label

[IzaakWN]

Using #minus in ROOT because - would just be a short hyphen.

Note that the guidelines recommends #font[122]{\55}, but #minus is more convenient, human readable, and native to ROOT. https://twiki.cern.ch/twiki/bin/viewauth/CMS/Internal/PubGuidelines Maybe we can suggest to PubComm to recommend #minus instead?

Below are screenshots from the PDF output:

Before, with hyphen -:

After, with the bit longer #minus:

And just for the record, this is with #font[122]{\55}, which seems to be a bit shorter, and also raises the superscript a bit?

[andrzejnovak]

Just for comparison, the current mplhep default looks like this. It seems to match the #minus suggestion. :)