Fixed bug in favicon location for footer

- vignettes triggered a warning about the missing
  favicon in the articles footer
- the path spec was a level off
- this fixes the issue; no more warnings and
  the logo is on all articles

_pkgdown.yml

@@ -23,7 +23,7 @@ footer:
     left: [logo, package, developed_by]
     right: built_with
   components:
-    logo: "<img src='favicon-16x16.png'>"
+    logo: "<img src='../favicon-16x16.png'>"
 
 template:
   bootstrap: 5