Default baud rate should take OS into account

[kenr]

The default baud rate when baud rate is not specified is 115200.
This baud rate is only relevant for macOS.

The open call should take the OS into account when setting a default baud rate:

pc-ble-driver-js/api/adapter.js

Line 380 in 6194a45

if (!options) {

[ghost]

the next version (i think) of pc-ble-driver will support larger baud rates on Mac OS

[bihanssen]

True, we could standardize on 1Mbps now that it is supported on all platforms.