Update pip and Skulpt installations for newer versions of Ubuntu (#6464)
Update pip and Skulpt installations for newer versions of Ubuntu (#6464)

* Update pip and Skulpt installation to work properly on newer versions of
Ubuntu.

* Address reviewer comment: try both pip installs.

* Clarify the new skulpt sed commands.

* Rearrange comments and clarify what the new disable lines are doing per
code review comments.

souravbadami/oppia,kevinlee12/oppia,prasanna08/oppia,prasanna08/oppia,kevinlee12/oppia,brianrodri/oppia,kevinlee12/oppia,oppia/oppia,kevinlee12/oppia,oppia/oppia,prasanna08/oppia,souravbadami/oppia,oppia/oppia,brianrodri/oppia,brianrodri/oppia,prasanna08/oppia,prasanna08/oppia,oppia/oppia,souravbadami/oppia,kevinlee12/oppia,souravbadami/oppia,brianrodri/oppia,oppia/oppia,souravbadami/oppia,brianrodri/oppia