Re-order upgrade instructions

composer update throws an error while executing artisan if you have not yet done this step:

- Remove call to `redirectIfTrailingSlash` in `bootstrap/start.php` file.
Merge pull request #2470 from adamgoose/develop

Re-order upgrade instructions
Enhancements to the 4.0>4.1 upgrade guide.
Merge pull request #2471 from adamgoose/develop

Enhancements to the 4.0>4.1 upgrade guide.