[FAB-10657] Fix typos in logging-control.rst

Fix typo in docs/source/logging-control.rst:
  "subcommmand" to "subcommand"
  "varaibles" to "variables"

Change-Id: I5d1cf18ca802501da968e1b2f47312a5c0289c9a
Signed-off-by: Daisuke IIZUKA <daisuke.iizuka.ag@hitachi.com>

Author: Daisuke IIZUKA

docs/source/logging-control.rst

@@ -57,9 +57,9 @@ The default logging level for each individual ``peer`` subcommand can
 also be set in the
 `core.yaml <https://github.com/hyperledger/fabric/blob/master/sampleconfig/core.yaml>`__
 file. For example the key ``logging.node`` sets the default level for
-the ``node`` subcommmand. Comments in the file also explain how the
+the ``node`` subcommand. Comments in the file also explain how the
 logging level can be overridden in various ways by using environment
-varaibles.
+variables.
 
 Logging severity levels are specified using case-insensitive strings
 chosen from