updated for mbed-os 5.5

Fork of Task324 by Nicholas Outram

Revision:
1:5d510a407d4c
Parent:
0:8ab606ae2e1d
--- a/mbed-os.lib	Thu Jul 13 14:48:03 2017 +0000
+++ b/mbed-os.lib	Wed Sep 11 14:42:50 2019 +0000
@@ -1,1 +1,1 @@
-https://github.com/ARMmbed/mbed-os/#8828635da469162cf2854b5287561c663fb96e72
+https://github.com/ARMmbed/mbed-os/#1bf6b20df9d3cd5f29f001ffc6f0d0fcbbb96118