Update mobileData validity values

Author: aksalj

README.md

@@ -171,7 +171,7 @@ Instantiating the class will give you an object with available methods
             - `phoneNumber`: Customer phone number (in international format). `REQUIRED`
             - `quantity`: Mobile data amount. `REQUIRED`
             - `unit`: Mobile data unit. Can either be `MB` or `GB`. `REQUIRED`
-            - `validity`: How long the mobile data is valid for. Must be one of `Daily`, `Weekly` and `Monthly`. `REQUIRED`
+            - `validity`: How long the mobile data is valid for. Must be one of `Day`, `Week` and `Month`. `REQUIRED`
             - `metadata`: Additional data to associate with the tranasction. `REQUIRED`
 
     - **$options:** optional associative array with the following keys:

src/Payments.php

@@ -586,8 +586,8 @@ protected function doMobileData($parameters, $options = [])
                 }
 
                 if (isset($r['validity'])) {
-                    if (!in_array($r['validity'], ['Daily', 'Monthly', 'Weekly'])) {
-                        return $this->error('validity must be one of Daily, Weekly, Monthly'); 
+                    if (!in_array($r['validity'], ['Day', 'Month', 'Week'])) {
+                        return $this->error('validity must be one of Day, Week, Month'); 
                     }
                 }