Upgraded deps (#3582)

Author: GrahamCampbell

composer.json

@@ -36,7 +36,8 @@
         "graham-campbell/core": "^5.1",
         "graham-campbell/exceptions": "^9.4",
         "graham-campbell/markdown": "^6.1",
-        "guzzlehttp/guzzle": "^6.2.1",
+        "guzzlehttp/guzzle": "6.3.3",
+        "guzzlehttp/psr7": "1.4.2",
         "jenssegers/date": "^3.2",
         "laravel/framework": "5.2.39",
         "mccool/laravel-auto-presenter": "^4.3",