flav-io/flavio v0.20.4

This point release fixes a few minor issues and adds or updates the following experimental measurements: Missing observables in the 2015 CMS measurement of B→K*μ⁺μ⁻ 2013 CMS measurement of B→K*μ⁺μ⁻ (which is statistically independent of the former) 2017 LHCb measurement of B_s→μ⁺μ⁻ updated to published version. Thanks to Marc Olivier Bettler and Flavio Archilli for useful correspondence and for providing the 2D likelihood data