Upgrade to the Latest Stack

[PeterDaveHello]

Warning from Heroku after each deployment

Warning: You are running on a deprecated stack.
Please upgrade to the latest stack by following the instructions on:
https://devcenter.heroku.com/articles/upgrading-to-the-latest-stack

[PeterDaveHello]

               _                  __ _  _     ______ ____  _
              | |                /_ | || |   |  ____/ __ \| |
   ___ ___  __| | __ _ _ __ ______| | || |_  | |__ | |  | | |
  / __/ _ \/ _` |/ _` | '__|______| |__   _| |  __|| |  | | |
 | (_|  __/ (_| | (_| | |         | |  | |   | |___| |__| | |____
  \___\___|\__,_|\__,_|_|         |_|  |_|   |______\____/|______|

This application is still using the Cedar-14 stack for which the end-of-life window began May 1, 2019:
https://devcenter.heroku.com/changelog-items/1603

The end-of-life window ends on May 1, 2020 after which Cedar-14 will no longer
receive security updates and Cedar-14 app builds will be disabled.

Please upgrade to the latest stack by following these instructions:
https://devcenter.heroku.com/articles/upgrading-to-the-latest-stack