Fix invalid CSS pseudo-element selector: `::hover` is invalid

[whoElseButUmar]

The stylesheet contains an invalid CSS selector using the pseudo-element syntax ::hover instead of the correct pseudo-class syntax :hover.

https://github.com/scrimba/learn-fullstack-development/blob/e2be3970a9ce2be58ef7375b8407b4831d825bb6/02. HTML and CSS Fundamentals/01. Intro to HTML/08. Let_s build Google/styles.css#L42