Make exceptions final

Author: sagikazarmark

src/Exception/ClientException.php

@@ -7,6 +7,6 @@
  *
  * @author Márk Sági-Kazár <[email protected]>
  */
-class ClientException extends HttpException
+final class ClientException extends HttpException
 {
 }

src/Exception/NetworkException.php

@@ -7,6 +7,6 @@
  *
  * @author Márk Sági-Kazár <[email protected]>
  */
-class NetworkException extends RequestException
+final class NetworkException extends RequestException
 {
 }

src/Exception/ServerException.php

@@ -7,6 +7,6 @@
  *
  * @author Márk Sági-Kazár <[email protected]>
  */
-class ServerException extends HttpException
+final class ServerException extends HttpException
 {
 }