core: Update the commons-lang 2.6

This is the version that we are using in deployments as it is included
in Fedora, just need to sync the POM to use it as well.

Change-Id: I110a7d1f8fb7178d0ad8a0900fbc73af4a9bac69
Signed-off-by: Juan Hernandez <juan.hernandez@redhat.com>