Problem solved!
I feel so stupid now. I had read that stackoverflow post before i wrote here AND tried with both of the jQuery sources below. The jQuery slim was located at the bottom of my HTML and not at the top where i was working. I´ll let this serve as a lesson to be cautious when trying to save time and reusing HTML from previous projects.
Thanks!
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script> <script src="https://code.jquery.com/jquery-3.1.1.min.js"></script>