Update Zip::File.open to rubyzip 3.0.0

Author: jochenehret

spec/support/test_zip.rb

@@ -2,7 +2,7 @@
 
 module TestZip
   def self.create(zip_name, file_count, file_size=1024, &blk)
-    Zip::File.open(zip_name, Zip::File::CREATE) do |zipfile|
+    Zip::File.open(zip_name, create: true) do |zipfile|
       file_count.times do |i|
         zipfile.get_output_stream("ziptest_#{i}") do |f|
           f.write('A' * file_size)