libGL.so.1: cannot open shared object file: No such file or directory

Trying to run this image - wills2133/tbpp

when trying to import cv2 -
i get

libGL.so.1: cannot open shared object file: No such file or directory

suggested solutions online are - apt-get install -y libgl1-mesa-dev

But this is already installed. Any suggestions would be really helpful.Thanks in advance.