Exclude examples from the dist

[shaneikennedy]

Is your feature request related to a problem? Please describe.

When you install pipenv you are getting the examples/ directory in this project which includes a Pipfile and it's lock file, and some security scanners will start reporting the packages declared in these as vulnerabilities (even thought the packages only get installed if you pipenv sync).

Describe the solution you'd like

Don't include the examples directory in the distribution

Describe alternatives you've considered

Keeping the examples/Pipfile.lock updated is an alternative but I don't think it needs to be included in the dist in the first place