fix image links

_imagemeta/feinstaub1.markdown

 ---
 title: "Feinstaubsensor (I)"
-picurl: "https://chaotikum.org/_media/undefined:20170910-img_4773.jpg"
+picurl: "https://wiki.chaotikum.org/_media/undefined:20170910-img_4773.jpg"
 description: "Feinstaubssensor-Set mit NODE MCU, weiteren Sensoren und Kabeln"
 author: "Lukas Ruge"
 license: "<a href='https://creativecommons.org/licenses/by-nc/4.0/de/'>CC BY NC</a>"

_imagemeta/feinstaub2.markdown

 ---
 title: Feinstaubsensor (II)
-picurl: https://chaotikum.org/_media/projekte:vortraege:feinstaub2.jpg
+picurl: "https://wiki.chaotikum.org/_media/projekte:vortraege:feinstaub2.jpg"
 description: Feinstaubsensor auf einem Balkon
 author: "Lukas Ruge"
 license: "<a href='https://creativecommons.org/licenses/by-nc/4.0/de/'>CC BY NC</a>"

_imagemeta/feinstaub3.markdown

 ---
 title: Feinstaubsensor (III)
-picurl: https://chaotikum.org/_media/projekte:vortraege:feinstaub3.jpg
+picurl: "https://wiki.chaotikum.org/_media/projekte:vortraege:feinstaub3.jpg"
 description: Feinstaub Sensor an einer Wand
 author: "Lukas Ruge"
 license: "<a href='https://creativecommons.org/licenses/by-nc/4.0/de/'>CC BY NC</a>"