Fix generator name used in testDeprecatedSniffsListDoesNotShowNeedsCsMode()

This test is about ensuring that deprecated sniffs messages are not
displayed when viewing sniff documentation, and it was added in 2507c78
(see #281).
Before, passing any value to the `generator` parameter was enough and
so, probably due to a typo, `text` was passed which does not correspond
to a valid generator.

The code being tested only checks if `Config::generator` is not `null`:

https://github.com/PHPCSStandards/PHP_CodeSniffer/blob/2507c78d6aa8fe714b19d5e62519cd75f0a3aceb/src/Ruleset.php#L343

Now that `Config` throws an exception when an invalid generator is
passed. The test had to be adjusted to use a valid generator name.

Author: rodrigoprimo

tests/Core/Ruleset/ShowSniffDeprecationsTest.php

@@ -153,7 +153,7 @@ public static function dataDeprecatedSniffsListDoesNotShowNeedsCsMode()
         return [
             'Standard using deprecated sniffs; documentation is requested' => [
                 'standard'       => __DIR__.'/ShowSniffDeprecationsTest.xml',
-                'additionalArgs' => ['--generator=text'],
+                'additionalArgs' => ['--generator=Text'],
             ],
         ];