Refer to fully qualified class names in PHPDoc (#232)
Refer to fully qualified class names in PHPDoc (#232)

Because this class is in `namespace Braintree;`, the old PHPDoc is referring to `Braintree\Braintree_Result_Successful`, which doesn't exist.

This would cause minor issues with IDE suggestions and static analyzers.

An alternate acceptable fix would be to change this to \Braintree_Result_Successful, but that isn't used elsewhere

These class references were defined by class_alias:

```
lib/Braintree/Result/Successful.php
92:class_alias('Braintree\Result\Successful', 'Braintree_Result_Successful');

lib/Braintree/Result/Error.php
123:class_alias('Braintree\Result\Error', 'Braintree_Result_Error');
```
inewswire/braintree_php,braintree/braintree_php,inewswire/braintree_php,inewswire/braintree_php,braintree/braintree_php,braintree/braintree_php