in the map JS code, find the following code:
var request = {
origin: fromAddress.full,
destination: address.full,
travelMode: google.maps.TravelMode.DRIVING
};
and change it to:
var request = {
origin: fromAddress.full,
destination: address.full,
travelMode: google.maps.TravelMode.DRIVING,
unitSystem: google.maps.UnitSystem.IMPERIAL
};