[ruby/fileutils] Bump up fileutils version to 1.6.0

https://github.com/ruby/fileutils/commit/918d19e4f2

lib/fileutils.rb

@@ -102,7 +102,7 @@ end
 # <tt>:verbose</tt> flags to methods in FileUtils.
 #
 module FileUtils
-  VERSION = "1.5.0"
+  VERSION = "1.6.0"
 
   def self.private_module_function(name)   #:nodoc:
     module_function name