fix: when PDF export options were included in @convert_to

Author: Masamitsu Ogura

lib/libreconv.rb

@@ -113,7 +113,7 @@ def escaped_source_path
 
     # @return [String]
     def target_filename
-      File.basename(escaped_source_path, '.*') + '.' + File.basename(@convert_to, ':*')
+      File.basename(escaped_source_path, '.*') + '.' + File.basename(@convert_to.split(':').first)
     end
 
     # @raise [IOError] If soffice headless command line tool not found.