Fix #2945: Reference correct options variable

plugins/guests/linux/cap/mount_virtualbox_shared_folder.rb

@@ -64,7 +64,7 @@ module VagrantPlugins
 
           # Chown the directory to the proper user. We skip this if the
           # mount options contained a readonly flag, because it won't work.
-          if !opts[:mount_options].include?("ro")
+          if !options[:mount_options].include?("ro")
             chown_commands = []
             chown_commands << "chown #{mount_uid}:#{mount_gid} #{expanded_guest_path}"
             chown_commands << "chown #{mount_uid}:#{mount_gid_old} #{expanded_guest_path}"