Bump phpunit minimum version

composer.json

@@ -25,7 +25,7 @@
         "php-amqplib/php-amqplib": "~2.4",
         "php-console/php-console": "^3.1.3",
         "phpspec/prophecy": "^1.6.1",
-        "phpunit/phpunit": "^7.3",
+        "phpunit/phpunit": "^7.5",
         "predis/predis": "^1.1",
         "rollbar/rollbar": "^1.3",
         "ruflin/elastica": ">=0.90 <3.0",