Expanded compatibility

Author: vesper8

composer.json

@@ -11,12 +11,12 @@
   },
 
   "require": {
-      "guzzlehttp/guzzle": "~6.0"
+      "guzzlehttp/guzzle": "~6.0|~7.0"
   },
 
   "autoload": {
     "psr-4": {
       "Sightengine\\": "src/"
     }
   }
-}
+}