Update PHP version and SDK version

Author: BushraAsif

README.md

@@ -26,7 +26,7 @@ try {
 
 ## Requirements
 
-The AltaPay API PHP requires PHP 5.6.0 or greater with the following extensions installed:
+The AltaPay API PHP requires PHP 7.0 or greater with the following extensions installed:
 
 - date
 - filter

src/AbstractApi.php

@@ -55,7 +55,7 @@ abstract class AbstractApi
     /**
      * PHP API version
      */
-    const PHP_API_VERSION = '3.5.0';
+    const PHP_API_VERSION = '3.5.1';
 
     /**
      * Event dispatcher