Upgrade papermill

[Philmod]

http://b/176254901

It wasn't upgraded in the latest prerelease image.

$ docker run -it gcr.io/kaggle-images/python:prerelease /bin/bash
root@322557b5cb60:/# papermill --version
2.1.0 from /opt/conda/lib/python3.7/site-packages/papermill/cli.py (3.7.6)
root@322557b5cb60:/# pip install --upgrade papermill
[...]
Successfully installed papermill-2.2.2
root@322557b5cb60:/# papermill --version
2.2.2 from /opt/conda/lib/python3.7/site-packages/papermill/cli.py (3.7.6)

[rosbo]

#934 will upgrade the base image which includes papermill 2.2.2. Probably better to not upgrade it here to avoid churn on the image as much as possible during the build process.