more accurate account of bash wildcard expansion (when nothing matches)

An epsilon size step for SWC but the last step for me to join the instructors.

In addition to the change in part 04 of the shell section I also changed the introduction of wildcards in part 03, didn't anticipate this when creating the branch name, sorry.

Thanks to @vahtras for solving the jekyll issue, I faced the same issue when trying make site and make check, but it all runs sucessfully now.