Replace Riot with Element in docs and comments

This only covers the simple cases of references to issues and repos. More
complex areas, such as deployment scripts, will be handled separately.

Part of https://github.com/vector-im/element-web/issues/14864

src/components/views/groups/GroupTile.js

@@ -126,7 +126,7 @@ const GroupTile = createReactClass({
         }
 
         // XXX: Use onMouseDown as a workaround for https://github.com/atlassian/react-beautiful-dnd/issues/273
-        // instead of onClick. Otherwise we experience https://github.com/vector-im/riot-web/issues/6156
+        // instead of onClick. Otherwise we experience https://github.com/vector-im/element-web/issues/6156
         return <AccessibleButton className="mx_GroupTile" onMouseDown={this.onMouseDown} onClick={nop}>
             { avatarElement }
             <div className="mx_GroupTile_profile">