Add missing dependency to slf4j-log4j bridge

Without the bridge JGit tests don't show log output in Eclipse console.

Change-Id: I7acce1f1787960b5ca98377cb5c7f599a8a220b5
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.test/build.properties

@@ -5,4 +5,5 @@ source.. = tst/,\
 bin.includes = META-INF/,\
                .,\
                plugin.properties
-additional.bundles = org.apache.log4j
+additional.bundles = org.apache.log4j,\
+                     org.slf4j.impl.log4j12