Issue description

pipenv shell can not activate custom virtualenv created by virtualenv

Actual result

➜  abcd  . /Users/jxltom/.local/share/virtualenvs/abcd-Gj3qkKPD/bin/activate
.: no such file or directory: /Users/liujunxiao/.local/share/virtualenvs/abcd-Gj3qkKPD/bin/activate

Steps to replicate

• virtualenv somedir
• cd somedir && source bin/activate
• pipenv shell

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