pip listのwarning(DEPRECATION)対応

pip９系でwarningが出るようになった

$ pip -V
pip 9.0.1

$ pip list
DEPRECATION: The default format will switch to columns in the future. You can use --format=(legacy|columns) (or define a format=(legacy|columns) in your pip.conf under the [list] section) to disable this warning.
Flask (0.12)
.
.

対応内容
https://pip.pypa.io/en/stable/user_guide/#config-file

$ vi ~/.pip/pip.conf
[list]
format = columns

$ pip list
Package  Version
-------- --------
Flask    0.12
.
.