Move phpcs from squizlabs to phpcsstandards

PHP_Codesniffer is being abandoned by squizlabs. See:

squizlabs/PHP_CodeSniffer#3932

So it has been moved (copied, not transferred, not good, squizlabs)
to the PHPCSStandards organisation.

So this PR just moves us to start using the new organisation. Let's
see how things evolve.

composer.json

@@ -20,7 +20,7 @@
     ],
     "require": {
         "dealerdirect/phpcodesniffer-composer-installer": "^1.0.0",
-        "squizlabs/php_codesniffer": "^3.7.2",
+        "phpcsstandards/php_codesniffer": "^3.7.2",
         "phpcsstandards/phpcsextra": "^1.1.0",
         "phpcompatibility/php-compatibility": "dev-develop#0a17f9ed"
     },