gemrb: Update to 0.8.6

GemRB v0.8.6 (2019-11-24):
  New features:
    - more audio, especially in bg1 and pst
    - sndchann.2da support
    - using bags in stores, NPC breaking points, worldmap travel in pst

  Improved features:
    - better megamod and detectable spells compatibility
    - iwd2 and pst levelup, infopoints, gui feedback, dualclassing, ranges
    - verbal constants, (tobex) opcodes, falling, paperdolls, projectiles
    - pst area animations, multipalette animations
    - bugfixes

(nia)