Problem interfacing Heart Rate Sensor (Pulse Sensor) with Arduino Mega 2560

Hi,
I have experience of interfacing Arduino Mega 2560 / Adruino Mega Adk with Pulse Rate Sensor (purchased from www.pulsesensor.com, As it was part of My Final Year Project.
Now I am trying to interface The same pulse sensor with Arduino Mega 2560, & it gave me error
“Error compiling for Board Arduino/Genuino Mega or Mega 2560”
I am using Windows 10 & Arduino IDE 1.8.3
Attached is the screen shot of the error…

The code is taken from Github…

Any help appreciated. Thanks alot