genomehubs/genomehubs: 2.4.21

Commits 3802e56: Allow relabelling of categories on x axis (Richard Challis) #193 8d7150f: Allow relabelling of categories on reports (Richard Challis) #193 76e4263: Fix label display/ fitting for histograms (Richard Challis) #194 3ca310f: Fix mismatch between scatter points and category legends (Richard Challis) #195 0f38533: allow for empty oxOpts when updating limits (Richard Challis) #195 6cadc5f: bump UI/API version (Richard Challis) 097f782: "Bump version: 2.4.20 → 2.4.21" (Richard Challis