Update PHP requirement, fix composer typo (#29)

This package depends upon `gliterd/backblaze-b2` which requires PHP 7.2.

Author: mlambley

.scrutinizer.yml

@@ -30,4 +30,4 @@ tools:
 build:
     environment:
         php:
-            version: 7.1
+            version: 7.2

composer.json

@@ -14,11 +14,11 @@
         }
     ],
     "require": {
-        "php": "^7.1.8",
+        "php": "^7.2",
         "league/flysystem": "~1.0",
         "gliterd/backblaze-b2": ">=1.5.0",
         "psr/http-message-implementation": "*",
-        "mikey179/vfsStream": "*"
+        "mikey179/vfsstream": "*"
     },
     "require-dev": {
         "phpunit/phpunit" : "~4.0||~5.0",