Fix spawn_mine keybinding: change second key from "Control_R" to 2 for consistency

conf/keybinding_game.json

@@ -9,6 +9,6 @@
     "scroll_left": ["Left", 10],
     "scroll_right": ["Right", 11],
     "spawn_bomb": ["Space", 1],
-    "spawn_mine": ["Left Ctrl", "Control_R", 17],
+    "spawn_mine": ["Left Ctrl", 2, 17],
     "pause": ["P", 16]
 }