Add override qualifier to bad_optional_access::what() - fixes GCC -Wsuggest-override warning

Author: cuavas

include/sol/optional_implementation.hpp

@@ -657,7 +657,7 @@ namespace sol {
 	class bad_optional_access : public std::exception {
 	public:
 		bad_optional_access() = default;
-		const char* what() const noexcept {
+		const char* what() const noexcept override {
 			return "Optional has no value";
 		}
 	};

single/include/sol/sol.hpp

@@ -4631,7 +4631,7 @@ namespace sol {
 	class bad_optional_access : public std::exception {
 	public:
 		bad_optional_access() = default;
-		const char* what() const noexcept {
+		const char* what() const noexcept override {
 			return "Optional has no value";
 		}
 	};