Simple LED blinking test code

Revision:
0:903ffe4d4440
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os.lib	Fri Jun 29 01:17:25 2018 +0000
@@ -0,0 +1,1 @@
+https://github.com/ARMmbed/mbed-os/#367dbdf5145f4d6aa3e483c147fe7bda1ce23a36