Update version

Author: Nyholm

composer.json

@@ -19,7 +19,7 @@
         "phpunit/phpunit": "^7.2.7",
         "symfony/http-foundation": "^3.4 || ^4.0",
         "zendframework/zend-diactoros": "^1.8",
-        "nyholm/psr7-server": "dev-interface",
+        "nyholm/psr7-server": "^0.1.2",
         "http-interop/http-factory-diactoros": "dev-master",
         "satooshi/php-coveralls": "^1.1"
     },