assets: update flot to 0.8.2

See https://github.com/flot/flot/releases/tag/v0.8.2 for release notes
flight.js: redraw baro only on time interval changes
Merge branch 'flot_0.8.2'
lib.xcsoar_.analysis: copy values instead of adding by reference

Avoid scoring_end to be overwritten if landing changes.