Rename image to match convention

The test was failing, and rather than do another back and forth
with the contributor I'm just gonna fix it up.

Author: ahpook

…servation/Bitmagasin_DigitalBevaring.png …al-preservation/digital-preservation.pngcollections/digital-preservation/Bitmagasin_DigitalBevaring.png renamed to collections/digital-preservation/digital-preservation.png collections/digital-preservation/Bitmagasin_DigitalBevaring.png renamed to collections/digital-preservation/digital-preservation.png

@@ -38,7 +38,7 @@ items:
 
 display_name: Digital Preservation
 created_by: ross-spencer
-image: Bitmagasin_DigitalBevaring.png
+image: digital-preservation.png
 ---
 
 Trying to look after the long-term preservation of your digital files? Get