Defaults: compare paths in applies_path? as Strings to avoid confusion

/cc #4064

lib/jekyll/frontmatter_defaults.rb

@@ -87,7 +87,7 @@ module Jekyll
 
       scope_path = Pathname.new(scope['path'])
       Pathname.new(sanitize_path(path)).ascend do |path|
-        if path == scope_path
+        if path.to_s == scope_path.to_s
           return true
         end
       end