Update RecruitHero.h

Fix warning.

AI/Nullkiller/Goals/RecruitHero.h

@@ -44,7 +44,7 @@ namespace Goals
 		}
 
 		std::string toString() const override;
-		const CGHeroInstance* getHero() { return heroToBuy; }
+		const CGHeroInstance* getHero() const override { return heroToBuy; }
 		void accept(AIGateway * ai) override;
 	};
 }