Fix package name

`mikey179/vfsStream` -> `mikey179/vfsstream`

Author: joelambert

composer.json

@@ -28,11 +28,11 @@
         "php-coveralls/php-coveralls": "^2.0",
         "mockery/mockery": "^1.0.0",
         "brain/monkey": "^2.2",
-	    "squizlabs/php_codesniffer": "^3.3.1",
+        "squizlabs/php_codesniffer": "^3.3.1",
         "php-mock/php-mock": "^2.0",
         "codedungeon/phpunit-result-printer": "^0.19.13",
         "codedungeon/php-cli-colors": "^1.10.7",
-        "mikey179/vfsStream": "^1.6",
+        "mikey179/vfsstream": "^1.6",
         "antecedent/patchwork": "^2.1.8"
     },
     "autoload": {