pipenv update --outdated generates no output

[yunti]

Issue description

pipenv update --outdated
generates no output.

Expected result

Something like 'all packages are upto date"

Actual result

It looks like it's working to check if anything is outdated and presumably finds nothing is outdated. However nothing is printed to the screen so no way to tell what has happened.

Steps to replicate

Provide the steps to replicate (which usually at least includes the commands and the Pipfile).

---

Please run $ pipenv --support, and paste the results here. Don't put backticks (`) around it! The output already contains Markdown formatting.

If you're on macOS, run the following:

$ pipenv --support | pbcopy

If you're on Windows, run the following:

> pipenv --support | clip

If you're on Linux, run the following:

$ pipenv --support | xclip