💄 Cast der_signature.length() to 'long' to silence compile warning (#270)

Co-authored-by: Dominik Thalhammer <[email protected]>

Author: gizmocuz

include/jwt-cpp/jwt.h

@@ -1215,7 +1215,8 @@ namespace jwt {
 			std::string der_to_p1363_signature(const std::string& der_signature, std::error_code& ec) const {
 				const unsigned char* possl_signature = reinterpret_cast<const unsigned char*>(der_signature.data());
 				std::unique_ptr<ECDSA_SIG, decltype(&ECDSA_SIG_free)> sig(
-					d2i_ECDSA_SIG(nullptr, &possl_signature, der_signature.length()), ECDSA_SIG_free);
+					d2i_ECDSA_SIG(nullptr, &possl_signature, static_cast<long>(der_signature.length())),
+					ECDSA_SIG_free);
 				if (!sig) {
 					ec = error::signature_generation_error::signature_decoding_failed;
 					return {};