pip 10.x adjusts where its internals are situated. The pip3 command you're seeing is one provided by your package maintainer (presumably debian based here?) and is not a file managed by pip.
You can read more about this on pip's issue tracker
Workaround
Again, from the above StackOverflow post - you need to downgrade to an earlier version of pip until this is resolved in Debian / Ubuntu.
To reproduce
Once upgraded:
Problem
According to a StackOverflow post:
Workaround
Again, from the above StackOverflow post - you need to downgrade to an earlier version of pip until this is resolved in Debian / Ubuntu.
Now run the install again: