修复一个编译警告

skywalking-api/src/main/java/com/ai/cloud/skywalking/plugin/interceptor/MethodMatcher.java

@@ -70,7 +70,7 @@ public abstract class MethodMatcher {
     public enum Modifier {
         Public, Default, Private, Protected;
 
-        private ElementMatcher elementMatcher() {
+        private ElementMatcher.Junction<MethodDescription> elementMatcher() {
             switch (this) {
                 case Private: {
                     return isPrivate();