AP_L1_Control: Fix NAVL1_PERIOD description typo

libraries/AP_L1_Control/AP_L1_Control.cpp

@@ -7,7 +7,7 @@ extern const AP_HAL::HAL& hal;
 const AP_Param::GroupInfo AP_L1_Control::var_info[] = {
     // @Param: PERIOD
     // @DisplayName: L1 control period
-    // @Description: Period in seconds of L1 tracking loop. This parameter is the primary control for agressiveness of turns in auto mode. This needs to be larger for less responsive airframes. The default is quite conservative, but for most RC aircraft will lead to reasonable flight. For smaller more agile aircraft a value closer to 15 is appropriate, or even as low as 10 for some very agile aircraft. When tuning, change this value in small increments, as a value that is much too small (say 5 or 10 below the right value) can lead to very radical turns, and a risk of stalling.
+    // @Description: Period in seconds of L1 tracking loop. This parameter is the primary control for aggressiveness of turns in auto mode. This needs to be larger for less responsive airframes. The default is quite conservative, but for most RC aircraft will lead to reasonable flight. For smaller more agile aircraft a value closer to 15 is appropriate, or even as low as 10 for some very agile aircraft. When tuning, change this value in small increments, as a value that is much too small (say 5 or 10 below the right value) can lead to very radical turns, and a risk of stalling.
     // @Units: s
     // @Range: 1 60
     // @Increment: 1