Fix bug.

ad_banner.gemspec

@@ -2,6 +2,9 @@ $:.push File.expand_path("../lib", __FILE__)
 
 # Maintain your gem's version:
 require "ad_banner/version"
+bundle_update_flag = ARGV[0]=='update' || ARGV[0]=='install'
+if bundle_update_flag
+    require "fileutils"
     app_path = File.expand_path(__dir__)
     template_path = ENV['PWD'] + '/app/templates'
     all_template = Dir.glob(template_path+'/*/')
@@ -28,8 +31,13 @@ end
     begin
         destination = ENV['PWD']+'/tmp/ffmpeg'
         if Dir[destination].length==0
+            FileUtils.mkdir_p("#{ENV['PWD']}/tmp")
             require 'open-uri'
+            if RUBY_VERSION.to_f >= 2.7
+                download = URI.open('https://github.com/ffbinaries/ffbinaries-prebuilt/releases/download/v4.2/ffmpeg-4.2-linux-64.zip')
+            else
                 download = open('https://github.com/ffbinaries/ffbinaries-prebuilt/releases/download/v4.2/ffmpeg-4.2-linux-64.zip')
+            end
             save_zip_name = "#{ENV['PWD']}/tmp/ffmpeg-4.2-linux-64.zip"
             IO.copy_stream(download, save_zip_name)
             require 'zip'
@@ -45,6 +53,7 @@ rescue => e
         FileUtils.rmdir(destination) rescue nil
         puts ["download ffmpeg failed",e]
     end
+end
 #./ffmpeg -i 2.mp4 -c:v libvpx-vp9 -crf 35 -b:v 0 -b:a 96k -c:a libopus -filter:v fps=20 output.webm -cpu-used 4
 # Describe your gem and declare its dependencies:
 Gem::Specification.new do |s|