Error refrence added

Error "imap_fetchheader(): Bad message number" refrence added

Author: Webklex

README.md

@@ -818,6 +818,7 @@ Extends [Illuminate\Support\Collection::class](https://laravel.com/api/5.4/Illum
 | imap_open(): Couldn't open (...) Please log in your web browser: (...)    | In order to use IMAP on some services (such as Gmail) you need to enable it first. [Google help page]( https://support.google.com/mail/answer/7126229?hl=en) |
 | imap_headerinfo(): Bad message number                                     | This happens if no Message number is available. Please make sure Message::parseHeader() has run before |
 | imap_open(): Couldn't open stream {outlook.office365.com:993/imap/s (...) | Can be caused by a lot of things: head over to these issues for more information: [#153](https://github.com/Webklex/laravel-imap/issues/153) [#100](https://github.com/Webklex/laravel-imap/issues/100) [#78](https://github.com/Webklex/laravel-imap/issues/78)  |
+| imap_fetchheader(): Bad message number | Try to change the `message_key` [#243](https://github.com/Webklex/laravel-imap/issues/243)
 
 ## Milestones & upcoming features
 * Wiki!!