Revert "Reverses subtraction in character.cpp to correct skill rust c…

…alculation"

This reverts commit 638126c.

src/character.cpp

@@ -4117,7 +4117,7 @@ int Character::rust_rate() const
     int intel = get_int();
     /** @EFFECT_INT reduces skill rust by 10% per level above 8 */
     int ret = ( ( rate_option == "vanilla" || rate_option == "capped" ) ?
-                100 : 100 + 10 * ( 8 - intel ) );
+                100 : 100 + 10 * ( intel - 8 ) );
 
     ret *= mutation_value( "skill_rust_multiplier" );