[BUGFIX] Require phpspec/prophecy as dev dependency

Author: IchHabRecht

composer.json

@@ -36,7 +36,8 @@
     },
     "require-dev": {
         "phpunit/phpunit": ">=6.0 <10.0",
-        "symfony/filesystem": ">=2.7 <7.0"
+        "symfony/filesystem": ">=2.7 <7.0",
+        "phpspec/prophecy": "^1.0"
     },
     "suggest": {
         "friendsofphp/php-cs-fixer": "Tool to automatically fix PHP coding standards issues"