fix composer.json (#50)

Author: Mararok

composer.json

@@ -12,7 +12,7 @@
     "phpunit/phpunit": "6.*",
     "mockery/mockery": "1.1.*",
     "codeclimate/php-test-reporter": "dev-master",
-    "mikey179/vfsStream": "1.6.*",
+    "mikey179/vfsstream": "1.6.*",
     "guzzlehttp/guzzle": "~6.0",
     "nannehuiges/jsend": "2.1.*",
     "monolog/monolog": "1.*",