qa: require prophecy 1.9 or greater

To ensure we work with PHP 7.4.

Author: michalbundyra

composer.json

@@ -32,6 +32,9 @@
     "phpunit/phpunit": "^5.7.16 || ^6.0.8 || ^7.2.7",
     "zendframework/zend-coding-standard": "~1.0"
   },
+  "conflict": {
+    "phpspec/prophecy": "<1.9.0"
+  },
   "provide": {
     "psr/http-message-implementation": "1.0"
   },