mejora realizada a la lectura de parametros del envio de sms

se agrega content type

src/AppBundle/Model/Sms.php

@@ -76,6 +76,7 @@ class Sms extends BaseSms
                 curl_setopt($ch, CURLOPT_SSL_VERIFYPEER,false);
                 curl_setopt($ch, CURLOPT_HTTPHEADER,
                 array(
+                "Content-Type: application/xml",    
                 "Accept: application/json",
                 "Authorization: Basic ".base64_encode($user.":".$password)));
                 curl_setopt($ch, CURLINFO_HEADER_OUT, true);