Fix not found ShortcodeTest class by the autoloader

[FabianSchmick]

If you extend the Webfactory\ShortcodeBundle\Tests\Functional\ShortcodeTest class as recommended in the README.md you will recieve an error which tells you, that the class could not be found.

This is because of:

    "autoload-dev": {
        "psr-4": {
            "Webfactory\\ShortcodeBundle\\Tests\\": "tests"
        }
    },

which will not load the class if the bundle is installed as a dependency.

This bug was found with the help of @mpdude maybe you want to extend my explanation?

[MalteWunsch]

I don't think it's a good idea to move test code into the production directory/production autoloading. This e.g. will lead to problems with composer-require-checker. What do you think about extending the "Automated Tests for your Shortcodes" section in the README.md instead with something like:

Include the folliwing in your composer.json:

"autoload-dev": {
       "psr-4": {
           "Webfactory\\ShortcodeBundle\\Tests\\": "vendor/webfactory/shortcode-bundle/tests"
       }
   },

?