Revert gsub!

Author: jvazquez-r7

modules/exploits/linux/http/synology_dsm_sliceupload_exec_noauth.rb

@@ -121,7 +121,7 @@ def exploit
     post_body.sub!(cmd_placeholder, cmds)
 
     # fix multipart encoding
-    post_body.gsub!(/\r\n\r\n--_Part/, "\r\n--_Part")
+    post_body.gsub!(/\r\n(--#{mime_msg.bound})/, '  \\1')
 
     # send request to append shell commands
     print_status("#{peer} - Injecting the payload...")