Correct semver

Author: Jose Zamora

lib/SparkPost/SparkPost.php

@@ -13,7 +13,7 @@ class SparkPost
     /**
      * @var string Library version, used for setting User-Agent
      */
-    private $version = '2.1.1';
+    private $version = '2.2.0';
 
     /**
      * @var HttpClient|HttpAsyncClient used to make requests