Update PHPUnit to version 9.

Author: chrisryan

composer.json

@@ -37,9 +37,8 @@
         "symfony/process": "~3.0"
     },
     "require-dev": {
-      "phpunit/phpunit": "~6.0",
-      "squizlabs/php_codesniffer": "~2.6",
-      "traderinteractive/coding-standard": "2.1.0"
+      "phpunit/phpunit": "^9.0",
+      "squizlabs/php_codesniffer": "^3.7"
     },
     "bin": ["bin/buildRelease"],
     "autoload": {