Version of pip is obsolete

[tk26eng]

A following warning message comes when we run the command of make build.

WARNING: You are using pip version 20.0.2; however, version 20.1 is available.
You should consider upgrading via the '/usr/local/pyenv/versions/3.6.3/envs/python3.6/bin/python -m pip install --upgrade pip' command.

[patrick-su]

@tk26eng just to be clear, do you want to suppress/hide the pip upgrade warning message when we run make build?

reference: https://stackoverflow.com/questions/46288847/how-to-suppress-pip-upgrade-warning

[tk26eng]

@patrick-su This might come from lack of cleaning cache. Please let me check it again after cleaning cache for docker.