The script assumes `pip` is available, generating `command not found` error.

[SamSirry]

Selecting to "Upgrade proxy software", line 190 generates an error:

https://github.com/HirbodBehnam/MTProtoProxyInstaller/blob/3c635ed09f48939e78297bf4a52376cee12dff01/MTProtoProxyInstall.sh#L190

MTProtoProxyInstall.sh: line 190: pip3.8: command not found

Perhaps the script should check before hand whether pip of this specific version is available on the system, or just run pip instead of pip3.8.