Reduce clicking noise on microphone acivation

Author: finneyj

source/MicroBitAudio.cpp

@@ -109,6 +109,7 @@ void MicroBitAudio::activateMic(){
     runmic.setDigitalValue(1);
     runmic.setHighDrive(true);
     adc.activateChannel(mic);
+    adc.getChannel(microphone, false)->setStartDelay(2);
     this->micEnabled = true;
 }