Update Candlepin to 4.8 for nightly (#1957)

Author: zjhuntin

vagrant/config/versions.yaml

@@ -139,7 +139,7 @@ installers:
 
   - foreman: 'nightly'
     katello: 'nightly'
-    candlepin: '4.7'
+    candlepin: '4.8'
     pulpcore: 'nightly'
     puppet: 8
     boxes: