fix files not being unzipped when 'ebook-extract' attribute is used

Unzipping was broken due to fixes for CVE-2018-1000544 in rubyzip: [1], [2].

Also, see [3].

[1]: rubyzip/rubyzip#371
[2]: rubyzip/rubyzip#376
[3]: rubyzip/rubyzip#354

lib/asciidoctor-epub3/converter.rb

@@ -30,7 +30,7 @@ def write output, target
                 unless (entry_dir = ::File.dirname entry.name) == '.' || (::File.directory? entry_dir)
                   ::FileUtils.mkdir_p entry_dir
                 end
-                entry.extract
+                entry.extract dest_path = entry.name
               end
             end
           end

spec/converter_spec.rb

@@ -31,6 +31,12 @@
       end
     end
 
+    it 'extracts book when given ebook-extract attribute' do
+      _, out_file = to_epub fixture_file('minimal/book.adoc'), attributes: { 'ebook-extract' => '' }
+      out_dir = out_file.dirname
+      expect(out_dir.join('book', 'EPUB', 'package.opf')).to exist
+    end
+
     it 'uses current date as fallback when date attributes cannot be parsed' do
       # TODO: assert that error log contains 'failed to parse revdate' error when we add test infrastructure for logs
       book, = to_epub fixture_file('minimal/book.adoc'), attributes: { 'revdate' => 'garbage' }