[ruby/tempfile] Bump up v0.3.1

https://github.com/ruby/tempfile/commit/297bdf2c8d

lib/tempfile.rb

@@ -157,7 +157,7 @@ require 'tmpdir'
 class Tempfile < DelegateClass(File)
 
   # The version
-  VERSION = "0.3.0"
+  VERSION = "0.3.1"
 
   # Creates a file in the underlying file system;
   # returns a new \Tempfile object based on that file.