Update to latest version of AEfremov kits.

Author: BranDougherty

Credits.md

@@ -1,4 +1,4 @@
 (very) Incomplete list of contributors and the assets they created:
 
-- AEfremov: shared/textures/objects/berserkerkit.png, shared/textures/objects/flamerkit.png, shared/textures/objects/predatorkit.png
+- AEfremov: shared/textures/objects/berserkerkit.png, shared/textures/objects/flamerkit.png, shared/textures/objects/predatorkit.png, shared/textures/objects/medikit.png
 - pewpew (@BranDougherty): shared/interface-gfx/friend.png, shared/interface-gfx/mic.png, shared/interface-gfx/connection.png