Added conflict version

Nyholm · Nyholm · commit 1091bb0d92f8 · 2018-03-05T12:41:00.000+01:00
diff --git a/composer.json b/composer.json
@@ -22,6 +22,9 @@
     "require-dev": {
         "phpunit/phpunit": "^6.0"
     },
+    "conflict": {
+        "phpunit/phpunit": "<6.0"
+    },
     "autoload": {
         "psr-4" : { "Matthias\\SymfonyDependencyInjectionTest\\" : "" }
     }
