Upping guzzle version to 6

Author: Khair-ed-Din Husseini

composer.json

@@ -4,8 +4,8 @@
     "license": "MIT",
     "require": {
         "php": ">=5.4.0",
-        "guzzlehttp/guzzle": "~5.0",
-        "commerceguys/guzzle-oauth2-plugin": "~2.0"
+        "guzzlehttp/guzzle": "^6",
+        "frankkessler/guzzle-oauth2-plugin": "dev-master"
     },
     "require-dev": {
         "phpspec/phpspec": "~2.0"
@@ -27,6 +27,12 @@
             "dev-master": "1.0-dev"
         }
     },
+    "repositories": [
+        {
+            "type": "vcs",
+            "url": "https://github.com/frankkessler/guzzle-oauth2-plugin.git"
+        }
+    ],
     "minimum-stability": "dev",
     "prefer-stable": true
 }