Update squizlabs/php_codesniffer requirement from ^3.5.6 to ^3.5.8

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@3.5.6...3.5.8)

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

composer.json

@@ -22,7 +22,7 @@
     "require-dev": {
         "phpunit/phpunit": "^7.5",
         "phpspec/prophecy": "^1.10",
-        "squizlabs/php_codesniffer": "^3.5.6"
+        "squizlabs/php_codesniffer": "^3.5.8"
     },
     "autoload": {
         "psr-4": {