Update lock.rst

incorrect assumption that $lock->getRemainingLifetime()'s unit was minutes instead of seconds

components/lock.rst

@@ -788,7 +788,7 @@ Using the above methods, a robust code would be::
  $lock->refresh();
  }
 
- // Perform the task whose duration MUST be less than 5 minutes
+ // Perform the task whose duration MUST be less than 5 seconds
  }
 
 .. caution::