docs: Fix broken links to React Conf videos (#3629)

Co-authored-by: Sebastian Silbermann <silbermann.sebastian@gmail.com>

Author: orama254

content/community/videos.md

@@ -13,12 +13,12 @@ Videos dedicated to the discussion of React and the React ecosystem.
 ### React Conf 2019 {#react-conf-2019}
 
 A playlist of videos from React Conf 2019.
-<iframe title="React Conf 2019" width="650" height="366" src="https://www.youtube-nocookie.com/embed/videoseries?list=PLPxbbTqCLbGHPxZpw4xj_Wwg8-fdNxJRh" frameborder="0" allowfullscreen></iframe>
+<iframe title="React Conf 2019" width="650" height="366" src="https://www.youtube-nocookie.com/embed/playlist?list=PLPxbbTqCLbGHPxZpw4xj_Wwg8-fdNxJRh" frameborder="0" allowfullscreen></iframe>
 
 ### React Conf 2018 {#react-conf-2018}
 
 A playlist of videos from React Conf 2018.
-<iframe title="React Conf 2018" width="650" height="366" src="https://www.youtube-nocookie.com/embed/videoseries?list=PLPxbbTqCLbGE5AihOSExAa4wUM-P42EIJ" frameborder="0" allowfullscreen></iframe>
+<iframe title="React Conf 2018" width="650" height="366" src="https://www.youtube-nocookie.com/embed/playlist?list=PLPxbbTqCLbGE5AihOSExAa4wUM-P42EIJ" frameborder="0" allowfullscreen></iframe>
 
 ### React.js Conf 2017 {#reactjs-conf-2017}