fix warnings and some reloading issues

modules/game_skills/skills.lua

@@ -59,6 +59,8 @@ function Skills.terminate()
   skillsButton = nil
   skillsWindow:destroy()
   skillsWindow = nil
+
+  Skills = nil
 end
 
 function Skills.toggle()

modules/game_skills/skills.otmod

@@ -4,6 +4,9 @@ Module
   author: OTClient team
   website: https://github.com/edubart/otclient
 
+  dependencies:
+    - game
+
   @onLoad: |
     dofile 'skills'
     Skills.init()