修改apiV3Key为非必填字段

Author: wujunjiesd

core/src/main/java/com/wechat/pay/java/core/RSAPublicKeyConfig.java

@@ -112,7 +112,6 @@ public RSAPublicKeyConfig build() {
       requireNonNull(publicKey);
       requireNonNull(publicKeyId);
       requireNonNull(privateKey);
-      requireNonNull(apiV3Key);
       requireNonNull(merchantSerialNumber);
 
       return new RSAPublicKeyConfig(this);