set the --rsyncable option for gzip

lib/backup/database.rb

@@ -17,7 +17,7 @@ module Backup
       FileUtils.mkdir_p(File.dirname(db_file_name))
       FileUtils.rm_f(db_file_name)
       compress_rd, compress_wr = IO.pipe
-      compress_pid = spawn(*%w(gzip -1 -c), in: compress_rd, out: [db_file_name, 'w', 0600])
+      compress_pid = spawn(*%w(gzip --rsyncable -1 -c), in: compress_rd, out: [db_file_name, 'w', 0600])
       compress_rd.close
 
       dump_pid =

lib/backup/files.rb

@@ -31,10 +31,10 @@ module Backup
           raise Backup::Error, 'Backup failed'
         end
 
-        run_pipeline!([%W(#{tar} --exclude=lost+found -C #{@backup_files_dir} -cf - .), %w(gzip -c -1)], out: [backup_tarball, 'w', 0600])
+        run_pipeline!([%W(#{tar} --exclude=lost+found -C #{@backup_files_dir} -cf - .), %w(gzip --rsyncable -c -1)], out: [backup_tarball, 'w', 0600])
         FileUtils.rm_rf(@backup_files_dir)
       else
-        run_pipeline!([%W(#{tar} --exclude=lost+found -C #{app_files_dir} -cf - .), %w(gzip -c -1)], out: [backup_tarball, 'w', 0600])
+        run_pipeline!([%W(#{tar} --exclude=lost+found -C #{app_files_dir} -cf - .), %w(gzip --rsyncable -c -1)], out: [backup_tarball, 'w', 0600])
       end
     end