Update the Slevomat Coding Standard version constraint

We are using the psr12Compatible option for the AlphabeticallySortedUses sniff,
but that is introduced in version 4.5.0.

Author: nicwortel

composer.json

@@ -14,7 +14,7 @@
         "dealerdirect/phpcodesniffer-composer-installer": "^0.4.4",
         "escapestudios/symfony2-coding-standard": "^3.0",
         "phpmd/phpmd": "^2.6",
-        "slevomat/coding-standard": "^4.3",
+        "slevomat/coding-standard": "^4.5",
         "squizlabs/php_codesniffer": "^3.0"
     },
     "require-dev": {