Update composer.json

Author: GrahamCampbell

composer.json

@@ -32,7 +32,7 @@
         "psr/http-client-implementation": "1.0"
     },
     "require-dev": {
-        "phpspec/phpspec": "^5.1 || ^6.0"
+        "phpspec/phpspec": "^5.1 || ^6.1 || ^7.3"
     },
     "config": {
         "sort-packages": true