upgrade guzzle version (#110)

Author: bpteam

composer.json

@@ -12,7 +12,7 @@
     ],
     "require": {
         "php": ">=5.5.0",
-        "guzzlehttp/guzzle": "^6.2"
+        "guzzlehttp/guzzle": "^6.2 | ^7.0"
     },
     "autoload": {
         "psr-4": {