Update squizlabs/php_codesniffer requirement from ^3.4.2 to ^3.5.5

Updates the requirements on [squizlabs/php_codesniffer](https://github.com/squizlabs/PHP_CodeSniffer) to permit the latest version.
- [Release notes](https://github.com/squizlabs/PHP_CodeSniffer/releases)
- [Commits](squizlabs/PHP_CodeSniffer@3.4.2...3.5.5)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

composer.json

@@ -23,7 +23,7 @@
         "phpunit/phpunit": "^7.5",
         "phpspec/prophecy": "^1.8",
         "phpstan/phpstan": "^0.11.5 || ^0.12.0",
-        "squizlabs/php_codesniffer": "^3.4.2"
+        "squizlabs/php_codesniffer": "^3.5.5"
     },
     "autoload": {
         "psr-4": {