Support Guzzle 7 (#294)

* Support Guzzle 7

Upgrade Guzzle version (needed for usage in Laravel 8)

* Update composer.json

Author: martijnb92

composer.json

@@ -18,12 +18,12 @@
     "test:syntax": "./vendor/bin/php-cs-fixer fix ./src --dry-run --stop-on-violation --using-cache=no"
   },
   "require": {
-    "php": "^7.2",
+    "php": ">=7.2",
     "ext-curl": "*",
     "ext-json": "*",
     "ext-mbstring": "*",
     "ext-openssl": "*",
-    "guzzlehttp/guzzle": "^6.2",
+    "guzzlehttp/guzzle": "^7.0.1|^6.2",
     "web-token/jwt-signature": "^2.0",
     "web-token/jwt-key-mgmt": "^2.0",
     "web-token/jwt-signature-algorithm-ecdsa": "^2.0",