Fix transposed UART RX/TX pins for RAK boards

This seems to have just been a typo. Fixing this allows RAK12500 to work in serial mode, and RAK12501 to work at all. (Both tested on RAK3401)

src/helpers/sensors/EnvironmentSensorManager.cpp

@@ -775,8 +775,7 @@ void EnvironmentSensorManager::initBasicGPS() {
 // or make a new location provider ...
 #ifdef RAK_WISBLOCK_GPS
 void EnvironmentSensorManager::rakGPSInit(){
-
-  Serial1.setPins(PIN_GPS_TX, PIN_GPS_RX);
+  Serial1.setPins(PIN_GPS_RX, PIN_GPS_TX);
 
   #ifdef GPS_BAUD_RATE
   Serial1.begin(GPS_BAUD_RATE);