Resolve hugo warnings

[florisdf]

Zorg dat volgende warnings niet meer Verschijnen bij het runnen van hugo:

WARN 2020/03/22 08:05:29 Page.RSSLink is deprecated and will be removed in a future release. 
Use the Output Format's link, e.g. something like:            
{{ with .OutputFormats.Get "RSS" }}{{ .RelPermalink }}{{ end }}                                          

WARN 2020/03/22 08:05:29 Page.URL is deprecated and will be removed in a future release. 
Use .Permalink or .RelPermalink. If what you want is the front matter URL value, use .Params.url.