Compare with nil when supplied argument is nil

- Avoid no method 'name' for nil error.
- The default spaceship operator also will return a nil instead of
  -1,0,1 if the objects provided are not comparable.
- coincidentally fixes a compatability issue seen with ruby 2.3.1

lib/fakes3/s3_object.rb

@@ -13,7 +13,7 @@ def eql?(object)
 
     # Sort by the object's name
     def <=>(object)
-      @name <=> object.name
+      @name <=> (object && object.name)
     end
   end
 end