Bump jetty from 6.1.14 to 6.1.23 in /tajo-core/tajo-core-backend

Bumps jetty from 6.1.14 to 6.1.23.

---
updated-dependencies:
- dependency-name: org.mortbay.jetty:jetty
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/tajo-core/tajo-core-backend/pom.xml b/tajo-core/tajo-core-backend/pom.xml
index d073736..7cc9c8e 100644
--- a/tajo-core/tajo-core-backend/pom.xml
+++ b/tajo-core/tajo-core-backend/pom.xml
@@ -406,7 +406,7 @@
     <dependency>
       <groupId>org.mortbay.jetty</groupId>
       <artifactId>jetty</artifactId>
-      <version>6.1.14</version>
+      <version>6.1.23</version>
     </dependency>
     <dependency>
       <groupId>org.mortbay.jetty</groupId>