Try to avoid `not delagated` error

```
.../ruby/lib/delegate.rb:405:in `__getobj__': not delegated (ArgumentError)
```
https://rubyci.org/logs/rubyci.s3.amazonaws.com/debian9/ruby-master/log/20190703T063006Z.fail.html.gz

lib/tempfile.rb

@@ -234,7 +234,7 @@ class Tempfile < DelegateClass(File)
 
   # :stopdoc:
   def inspect
-    if closed?
+    if @tmpfile.closed?
       "#<#{self.class}:#{path} (closed)>"
     else
       "#<#{self.class}:#{path}>"