Unable to reach github on Ubuntu wsl

I have just installed Ubuntu 18.04 (wsl) terminal on my Windows 10. It works fine but when I need to clone from github some repository, or to push, this error message is displayed:

Cloning into 'repo_name'...fatal: unable to access 'https://github.com/user/repo_name.git/': Could not resolve host: github.com

How can I fix it?

Thank you.