nrf52 serial and ble nano2 serial

Dependencies:  

Revision:
0:98aa84122685
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os.lib	Wed May 02 09:37:36 2018 +0000
@@ -0,0 +1,1 @@
+https://os.mbed.com/users/linuxsonu/code/mbed-os/#087a10df380b