Merge pull request #9 from prhost/master

fix - alguns providers estavam retornando not null porem com o endere…

src/CepGratis.php

@@ -101,7 +101,7 @@ public function resolve($cep)
         do {
             foreach ($this->providers as $provider) {
                 $address = $provider->getAddress($cep, $this->client, $this->options);
-                if (!is_null($address)) {
+                if (!is_null($address) && $address->state) {
                     break;
                 }
             }