Update dependencies

Author: baileyherbert

composer.json

@@ -15,10 +15,10 @@
     ],
     "require": {
         "php": ">=5.5",
-        "guzzlehttp/guzzle": "^6.3"
+        "guzzlehttp/guzzle": "^6.5.5"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8.35 || ^5.7 || ^6.4"
+        "phpunit/phpunit": "^4.8 || ^5.7 || ^6.5"
     },
     "autoload": {
         "psr-4": {