SITL: cap digits in LightWareSerial measurements

this was hitting the buffer-length limit in the ArduPilot rangefinder
driver as soon as we hit the 100m mark

libraries/SITL/SIM_RF_LightWareSerial.cpp

@@ -50,5 +50,5 @@ void RF_LightWareSerial::update(float range)
 
 uint32_t RF_LightWareSerial::packet_for_alt(uint16_t alt_cm, uint8_t *buffer, uint8_t buflen)
 {
-    return snprintf((char*)buffer, buflen, "%f\r", alt_cm / 100.0f); // note tragic lack of snprintf return checking
+    return snprintf((char*)buffer, buflen, "%0.2f\r", alt_cm / 100.0f); // note tragic lack of snprintf return checking
 }