#903 disable DOCTYPE to fix XXE Vulnerability

weixin-java-common/src/main/java/me/chanjar/weixin/common/util/crypto/WxCryptUtil.java

@@ -39,6 +39,7 @@ public class WxCryptUtil {
       try {
         final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
         factory.setExpandEntityReferences(false);
+        factory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
         return factory.newDocumentBuilder();
       } catch (ParserConfigurationException exc) {
         throw new IllegalArgumentException(exc);