Detect a HMC5883 magnetometer by reading the id registers for NUCLEO-L432KC

Revision:
0:10e9548cdb3d
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os.lib	Thu Aug 30 13:36:05 2018 +0000
@@ -0,0 +1,1 @@
+https://github.com/armmbed/mbed-os/#0fdfcf7350896a9c0b57c4a18237677abfe25f1a