practises/css-a-javscript: rename id of js section

Links (javascript) in the assignment https://sojka.pages.fi.muni.cz/PB029_web/miniwork/css-a-javascript/zadani.pdf didn't redirect us to the right place on the website because there was a different id in links than on the website. So, I checked the occurrences of this id in the code, and it seems safe to rename the id of the span.