Fix bug in dial action

The dial action should take an array of phone numbers and convert to a string.
Previously, it acted as though the phone numbers is a single string instead of an array of strings.

src/Voice.php

@@ -267,7 +267,7 @@ protected function buildDial($options)
         if (!isset($options['phoneNumbers'])) {
             return $this->error('Please specifiy at least one number to dial');
         }
-        $phoneNumbers = $options['phoneNumbers'];
+        $phoneNumbers = implode(", ", $options["phoneNumbers"]);
 
         // Check if ringback tone is set
         if (isset($options['ringbackTone'])) {
@@ -478,4 +478,4 @@ private function isValidURL($url)
         }
         return !filter_var($url, FILTER_VALIDATE_URL) === false;
     }
-}
+}