Bump prooph-v7-event-store version to 0.9

Author: Alexander Miertsch

composer.json

@@ -34,7 +34,7 @@
   "require-dev": {
     "phpunit/phpunit": "^7.0",
     "event-engine/php-json-schema": "^1.0",
-    "event-engine/prooph-v7-event-store": "^0.8",
+    "event-engine/prooph-v7-event-store": "^0.9",
     "bookdown/bookdown": "1.x-dev",
     "prooph/php-cs-fixer-config": "^0.3",
     "satooshi/php-coveralls": "^1.0",