Update ChainException to support Throwables

Fixes issue where TypeErrors, etc, would cause an exception without the relevant messages shown

src/Exception/ChainException.php

@@ -34,7 +34,7 @@ final class ChainException extends Exception
      */
     public function __construct(array $exceptions)
     {
-        $messages = array_map(function (\Exception $exception) {
+        $messages = array_map(function (\Throwable $exception) {
             return sprintf(
                 '%s: %s',
                 get_class($exception),