Fix a typo

message_definitions/v1.0/common.xml

@@ -1641,7 +1641,7 @@
         <param index="2" label="Force" minValue="0" maxValue="21196" increment="21196">0: arm-disarm unless prevented by safety checks (i.e. when landed), 21196: force arming/disarming (e.g. allow arming to override preflight checks and disarming in flight)</param>
       </entry>
       <entry value="401" name="MAV_CMD_RUN_PREARM_CHECKS" hasLocation="false" isDestination="false">
-        <description>Instructs system to run pre-arm checks.  This command should return MAV_RESULT_TEMPORARILY_REJECTED in the case the system is armed, otherwse MAV_RESULT_ACCEPTED.  Note that the return value from executing this command does not indicate whether the vehicle is armable or not, just whether the system has successfully run/is currently running the checks.  The result of the checks is reflected in the SYS_STATUS message.</description>
+        <description>Instructs system to run pre-arm checks. This command should return MAV_RESULT_TEMPORARILY_REJECTED in the case the system is armed, otherwise MAV_RESULT_ACCEPTED. Note that the return value from executing this command does not indicate whether the vehicle is armable or not, just whether the system has successfully run/is currently running the checks.  The result of the checks is reflected in the SYS_STATUS message.</description>
       </entry>
       <entry value="405" name="MAV_CMD_ILLUMINATOR_ON_OFF" hasLocation="false" isDestination="false">
         <wip/>