Following is the error that youtube-dl gave me. Another tool you-get gave me a similar error. What should I do to download videos from youtube.

[~] youtube-dl -f 137 https://youtu.be/0Ef9GudbxXY

17:27:23 [youtube] 0Ef9GudbxXY: Downloading webpage ERROR: Unable to download webpage: (caused by URLError(SSLError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:841)'),))