Fix add to my calendar button (#927)

Co-authored-by: Jesse Wright <63333554+jeswr@users.noreply.github.com>

Author: aalimsahin

community.html

@@ -174,7 +174,7 @@ <h2 property="schema:name">Events</h2>
                     center center no-repeat;
                 "
                 src="https://open-web-calendar.hosted.quelltext.eu/calendar.html?url=https%3A%2F%2Fwww.w3.org%2Fgroups%2Fwg%2Flws%2Fcalendar%2Fexport%2F&amp;url=https%3A%2F%2Fwww.w3.org%2Fgroups%2Fcg%2Fsolid%2Fcalendar%2Fexport%2F&amp;url=https%3A%2F%2Fcalendar.google.com%2Fcalendar%2Fical%2Fc_bfb1bff94af78734820e9fe79db6057dc445ae82fda9beb80b70cf67945df491%2540group.calendar.google.com%2Fpublic%2Fbasic.ics"
-                sandbox="allow-scripts allow-same-origin allow-top-navigation"
+                sandbox="allow-scripts allow-same-origin allow-top-navigation allow-downloads"
                 allowTransparency="true"
                 scrolling="no"
                 frameborder="0"

events.html

@@ -238,7 +238,7 @@ <h1 id="solid-events">Solid Events</h1>
 <iframe id="open-web-calendar" 
     style="background:url('https://raw.githubusercontent.com/niccokunzmann/open-web-calendar/master/static/img/loaders/circular-loader.gif') center center no-repeat;"
     src="https://open-web-calendar.hosted.quelltext.eu/calendar.html?url=https%3A%2F%2Fwww.w3.org%2Fgroups%2Fwg%2Flws%2Fcalendar%2Fexport%2F&amp;url=https%3A%2F%2Fwww.w3.org%2Fgroups%2Fcg%2Fsolid%2Fcalendar%2Fexport%2F&amp;url=https%3A%2F%2Fcalendar.google.com%2Fcalendar%2Fical%2Fc_bfb1bff94af78734820e9fe79db6057dc445ae82fda9beb80b70cf67945df491%2540group.calendar.google.com%2Fpublic%2Fbasic.ics"
-    sandbox="allow-scripts allow-same-origin allow-top-navigation"
+    sandbox="allow-scripts allow-same-origin allow-top-navigation allow-downloads"
     allowTransparency="true" scrolling="no" 
     frameborder="0" height="600px" width="100%"></iframe>