Fix a small typo in the Discovery Server documentation. (ros2#937)

Signed-off-by: Chris Lalancette <clalancette@openrobotics.org>

source/Tutorials/Discovery-Server/Discovery-Server.rst

@@ -168,7 +168,7 @@ Server Redundancy
 By using ``fastdds`` tool, multiple discovery servers can be created.
 Discovery clients (ROS nodes) can connect to as many servers as desired.
 This allows to have a redundant network that will work even if some servers or nodes shut down unexpectedly.
-The figure below shows a simple architecture that probide server redundancy.
+The figure below shows a simple architecture that provides server redundancy.
 
 .. image:: figures/ds_redundancy_example.svg
     :align: center