Update composer.json

Author: bashgeek

composer.json

@@ -21,7 +21,7 @@
     ],
     "require" : {
         "php" : ">=5.5",
-        "guzzlehttp/guzzle" : "^6.2"
+        "guzzlehttp/guzzle" : "^6.2|^7.0"
     },
     "autoload": {
         "psr-4": { "Amazon\\ProductAdvertisingAPI\\v1\\" : "src/" }