Fixing small typos in truth code from Higgs

The new collections are Bosons, rather than Boson.

At some point I'd love to hear from someone in the Higgs group about whether the navigation decorations are working for them. Naively I'd expected that adding the 'standard' collections (like W with decay products or HardScatter, which include vertices and particles) as well as the ones that are pure particles (Electrons, taus, etc) wouldn't work smoothly, but perhaps I was too pessimistic!

FYI @egramsta