add slf4j and log4j version

Signed-off-by: olivier lamy <olamy@apache.org>
diff --git a/pom.xml b/pom.xml
index 29154f8..c2e5474 100644
--- a/pom.xml
+++ b/pom.xml
@@ -77,6 +77,8 @@
     <svnkit.version>1.8.9</svnkit.version>
 
     <jetty.version>9.4.14.v20181114</jetty.version>
+    <slf4j.version>1.7.25</slf4j.version>
+    <log4j.version>2.9.1</log4j.version>
 
     <!-- reporting plugins versions -->
     <maven-project-info-reports-plugin.version>3.0.0</maven-project-info-reports-plugin.version>