[Security] Bump squizlabs/php_codesniffer from 2.8.0 to 3.3.1

Bumps [squizlabs/php_codesniffer](https://github.com/squizlabs/PHP_CodeSniffer) from 2.8.0 to 3.3.1. **This update includes security fixes.**
- [Release notes](https://github.com/squizlabs/PHP_CodeSniffer/releases)
- [Commits](squizlabs/PHP_CodeSniffer@2.8.0...3.3.1)

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

Author: dependabot-support

composer.json

@@ -18,7 +18,7 @@
     "require-dev": {
         "guzzlehttp/psr7": "^1.3",
         "phpunit/phpunit": "^6.0",
-        "squizlabs/php_codesniffer": "^2.6"
+        "squizlabs/php_codesniffer": "^3.3"
     },
     "autoload": {
         "psr-4": {