update ch.qos.logback:logback-core 1.2.3 to 1.2.8 (#1232)

diff --git a/dubbo-admin-server/pom.xml b/dubbo-admin-server/pom.xml
index 872c81c..a143b5c 100644
--- a/dubbo-admin-server/pom.xml
+++ b/dubbo-admin-server/pom.xml
@@ -263,7 +263,7 @@
         <dependency>
             <groupId>ch.qos.logback</groupId>
             <artifactId>logback-core</artifactId>
-            <version>1.2.3</version>
+            <version>1.2.8</version>
         </dependency>
     </dependencies>