Anlysis instead of Analyses

[jgbarah]

Minor issue, but a bit distubing... Analyses is plural, Analysis is singular. I guess we should use analysis/analysis.py and in it, Analysis, instead of analysis/analyses.py and Analyses (as we use, for example, Report for the corresponding class).
I can produce a pull request, if that's convenient (I checked, and at least in GrimoireLib there are just a few occurrences of the name).