Typo in ubuntu GSG
Typo in ubuntu GSG

- fixes typo in ubuntu.rst

Change-Id: I3f314cbf09602145757c28552f071e89132efe35
Closes-Bug: #1520493

stackforge/networking-ovs-dpdk,openstack/networking-ovs-dpdk,stackforge/networking-ovs-dpdk,stackforge/networking-ovs-dpdk,openstack/networking-ovs-dpdk