updated for mbed os 5.4

Revision:
1:cbcb7c2d43cd
Parent:
0:e48f4ddb9393
Child:
2:22ab4fcc5293
--- a/mbed-os.lib	Thu Mar 30 12:39:47 2017 +0000
+++ b/mbed-os.lib	Fri Sep 20 15:10:15 2019 +0000
@@ -1,1 +1,1 @@
-https://github.com/ARMmbed/mbed-os/#50b3418e45484ebf442b88cd935a2d5355402d7d
+https://github.com/ARMmbed/mbed-os/#1bf6b20df9d3cd5f29f001ffc6f0d0fcbbb96118