Fix categories not showing its list properly.

hugo.toml

@@ -53,9 +53,9 @@ theme = "hello-friend-ng"
   images = [""]
 
 [taxonomies]
-    category = "categories"
+    categories = "categories"
-    tag      = "tags"
+    tags       = "tags"
-    series   = "series"
+    series     = "series"
 
 [languages]
   [languages.en]