Revert accidental change to composer.json

Author: defuse

composer.json

@@ -27,8 +27,7 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^4|^5",
-        "nikic/php-parser": "^2.0|^3.0|^4.0",
-        "vimeo/psalm": "dev-master"
+        "nikic/php-parser": "^2.0|^3.0|^4.0"
     },
     "bin": [
         "bin/generate-defuse-key"