Upgrade to python3.8 to support mitmproxy 6 and TLS1.3

[fservida]

Mitm 6 requires python 3.8.
Until python3.8 is available, it is not possible to use MITMPROXY 6

Mitmproxy < 6 does not support TLS1.3 when writing to SSLkeylogfile in order to decrypt with Wireshark