Dependency updates etc. (#6)

* deps updated

* type hints added & travis php version updated

* [skip ci] phpunit configuration updated for 9.3 & fix authorize test

* [skip ci] fallback versions reverted & rollback php 7.4 features

composer.json

@@ -17,9 +17,9 @@
   "type": "library",
   "require": {
     "php": ">=7.1.3",
-    "guzzlehttp/guzzle": "^6.5",
+    "guzzlehttp/guzzle": "^6.5|^7.0.1",
     "symfony/http-foundation": "^4.4|^5.0",
-    "payconn/common": "~1.3.9"
+    "payconn/common": "~1.4"
   },
   "autoload": {
     "psr-4": {
@@ -38,10 +38,5 @@
     "phpunit/phpunit": "^7.3",
     "phpstan/phpstan": "^0.11.2",
     "vimeo/psalm": "^3.9"
-  },
-  "config": {
-    "platform": {
-      "php": "7.1.3"
-    }
   }
 }