You see this error because some other program is trying to update Ubuntu. When a command or application updates the system or installs new software, it locks the dpkg file (Debian package manager).
This locking is done so that two processes don’t change the content simultaneously, as it may lead to unwarranted situations and a possible broken system.
Check if some other program or application like Software Center or Software Updater is running system update or installing a program. If yes, wait for it to finish.
Then re-run the pip install command.
Try to follow the steps provided in the link and then restart the linux .It worked in my case.