build: change phpunit version

Changed the PHPUnit version from 9.0 to 9.5

Closes #17

Author: josantonius

composer.json

@@ -4,8 +4,8 @@
     "license": "MIT",
     "type": "library",
     "keywords": [
-        "Session",
-        "PHP"
+        "session",
+        "php"
     ],
     "authors": [
         {
@@ -25,7 +25,7 @@
     },
     "require-dev": {
         "phpmd/phpmd": "^2.12",
-        "phpunit/phpunit": "^9.0",
+        "phpunit/phpunit": "^9.5",
         "squizlabs/php_codesniffer": "^3.7"
     },
     "minimum-stability": "stable",