Random on and off blinky for nRF-DK

Revision:
0:774078f45f9d
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os.lib	Thu May 31 15:33:24 2018 +0000
@@ -0,0 +1,1 @@
+https://github.com/ARMmbed/mbed-os/#2885c1b41e63158cb6faf5f107cd821ae06ef26c