Merge pull request #49 from XeroAPI/update-xero-php-oauth2

Update xero-php-oauth2 to 8.0.0

Author: Raghunath-S-S-J

composer.json

@@ -3,7 +3,7 @@
   "description": "Xero OAuth 2.0 app for PHP",
   "type": "project",
   "require": {
-    "xeroapi/xero-php-oauth2": "7.1.0",
+    "xeroapi/xero-php-oauth2": "8.0.0",
     "monolog/monolog": "1.0",
     "vlucas/phpdotenv": "^4.1",
     "symfony/deprecation-contracts": "2.5.0"