Update jQuery to 3.5.0 (#458)

Author: karistom

site/layouts/partials/header.html

@@ -24,7 +24,7 @@
     <link href="{{"css/overrides.css" | relURL}}{{ if $assetBusting }}?{{ now.Unix }}{{ end }}" rel="stylesheet">
     <link href="https://fonts.googleapis.com/css?family=Almendra:700,400" rel="stylesheet">
 
-    <script src="{{"js/jquery-2.x.min.js"| relURL}}{{ if $assetBusting }}?{{ now.Unix }}{{ end }}"></script>
+    <script src="{{"js/jquery-3.5.0.min.js"| relURL}}{{ if $assetBusting }}?{{ now.Unix }}{{ end }}"></script>
 
     <style type="text/css">
       :root #header + #content > #left > #rlblock_left{ 

site/themes/learn/layouts/partials/header.html

@@ -21,7 +21,7 @@
       <link href="{{(printf "css/theme-%s.css" .) | relURL}}{{ if $assetBusting }}?{{ now.Unix }}{{ end }}" rel="stylesheet">
     {{end}}
 
-    <script src="{{"js/jquery-2.x.min.js"| relURL}}{{ if $assetBusting }}?{{ now.Unix }}{{ end }}"></script>
+    <script src="{{"js/jquery-3.5.0.min.js"| relURL}}{{ if $assetBusting }}?{{ now.Unix }}{{ end }}"></script>
 
     <style type="text/css">
       :root #header + #content > #left > #rlblock_left{