Serial passthrough tested on K64

Revision:
86:bb53196f7557
Parent:
85:b4c5dbbf74e3
--- a/mbed-os.lib	Wed Dec 19 13:45:03 2018 +0000
+++ b/mbed-os.lib	Tue Mar 31 08:42:42 2020 +0000
@@ -1,1 +1,1 @@
-https://github.com/ARMmbed/mbed-os/#6a0a86538c0b9b2bfcc4583b1e2b7fea8f4e71e9
+https://github.com/ARMmbed/mbed-os/#ecb3c8c837162c73537bd0f3592c6e2a42994045