Fix: Pip error when compiling Basilisk

[JulianHammerl]

I got an error when compiling Basilisk saying that "There was an error checking the latest version of pip". I fixed this by clearing pip's update cache using the following command:

Linux

rm -r ~/.cache/pip/selfcheck/

OSX

rm -r ~/Library/Caches/pip/selfcheck/

Windows

rm -r $env:LOCALAPPDATA\pip\cache\selfcheck\

More information can be found here.