add some @throws in constructors (#1779)

src/Monolog/Formatter/NormalizerFormatter.php

@@ -33,6 +33,7 @@ class NormalizerFormatter implements FormatterInterface
 
     /**
      * @param string|null $dateFormat The format of the timestamp: one supported by DateTime::format
+     * @throws \RuntimeException If the function json_encode does not exist
      */
     public function __construct(?string $dateFormat = null)
     {