SafeDetect / Mbed OS tx_serial_from_pi

this works for reading in data from pi via usb

Diff: mbed-os.lib

Revision:
102:630e8252eabf
Parent:
101:130fd2e532f0
--- a/mbed-os.lib	Wed Oct 23 18:00:04 2019 +0100
+++ b/mbed-os.lib	Tue Dec 10 04:04:03 2019 +0000
@@ -1,1 +1,1 @@
-https://github.com/ARMmbed/mbed-os/#679d24833acf0a0b5b0d528576bb37c70863bc4e
+https://github.com/ARMmbed/mbed-os/#c966348d3f9ca80843be7cdc9b748f06ea73ced0