Tweak Wagtail logo hover animation in docs

This matches the hover animation exactly the same as in Wagtail but without the "playful" wagtail Easter egg (where the original hover animation came from)

docs/_static/css/custom.css

@@ -34,8 +34,7 @@ div.wy-side-nav-search {
 }
 
 .logo:hover {
-    transform: rotate(8deg);
-    transition: transform 1.2s ease;
+    transform: rotate(4deg);
 }
 
 /* Wagtail Space */