SPISlave example not working

### Basic Infos

- [X ] This issue complies with the [issue POLICY doc](https://github.com/esp8266/Arduino/blob/master/POLICY.md).
- [ X] I have read the documentation at [readthedocs](https://arduino-esp8266.readthedocs.io/en/latest) and the issue is not addressed there.
- [ X] I have tested that the issue is present in current master branch (aka latest git).
- [ X] I have searched the issue tracker for a similar issue.
- [ X] If there is a stack dump, I have decoded it.
- [ X] I have filled out all fields below.

#### Platform

- Hardware: [ESP-12]
- Core Version: [latest git hash]
- Development Env: [Arduino IDE]
- Operating System: [Windows]

### Settings in IDE

- Module: [Nodemcu]
- Flash Mode: [qio]
- Flash Size: [4MB]
- lwip Variant: [v2 lower]
- Reset Method: [ck|nodemcu]
- Flash Frequency: [40Mhz]
- CPU Frequency: [80Mhz]
- Upload Using: [SERIAL]
- Upload Speed: [115200] (serial upload only)

### Problem Description

ESP Slave demo code not displaying data received from Master UNO.

Used below connection diagram for setting up UNO as master and nodemcu as Slave.
GPIO NodeMCU Name | Uno
===================================
15 D8 SS | D10
13 D7 MOSI | D11
12 D6 MISO | D12
14 D5 SCK | D13

### [MCVE](https://stackoverflow.com/help/mcve) Sketch
Compiled and uploaded below code into UNO
https://github.com/esp8266/Arduino/tree/master/libraries/SPISlave/examples/SPISlave_SafeMaster

Compiled and uploaded below code into NodeMCU

https://github.com/esp8266/Arduino/tree/master/libraries/SPISlave/examples/SPISlave_Test

### Debug Messages

Debug info received from UNO serial monitor
[
Master: Are you alive?
Slave:

Master: Are you alive?
Slave:
]

Debug ino displayed in NodeMCU serial monitor,
[
connected with ASUS-2.4g, channel 2
dhcp client start...
ip:192.168.2.251,mask:255.255.255.0,gw:192.168.2.1
pm open,type:2 0
]