try

announcement.gemspec

@@ -33,13 +33,16 @@ if old_gemfile_text != new_gemfile_text
   File.open(ENV['PWD']+'/Gemfile', 'w') do |file|
     file.write new_gemfile_text
   end
-  #a = Thread.new do
-  #  Bundler.with_clean_env do
-  #    system("bundle update")
-  #    puts 'test123'
-  #  end
-  #end
-  #a.join()
+  a = Thread.new do
+    Bundler.with_clean_env do
+      puts 'waiting'
+      Thread.stop
+      system("bundle update")
+      puts 'test123'
+    end
+  end
+  a.wakeup
+  a.join
   Thread.exit
 end
 # Describe your gem and declare its dependencies: