Update helium-us915 Example with Correct Sub Band

Author: kent-williams

examples/helium-us915/helium-us915.ino

@@ -305,7 +305,7 @@ void setup() {
 
     LMIC_setLinkCheckMode(0);
     LMIC_setDrTxpow(DR_SF7,14);
-    LMIC_selectSubBand(6);
+    LMIC_selectSubBand(2);
 
     // Start job (sending automatically starts OTAA too)
     do_send(&sendjob);