Add JSON_INVALID_UTF8_SUBSTITUTE flag to default json_encode flags, refs #1446, fixes #1203

src/Monolog/Utils.php

@@ -13,7 +13,7 @@ namespace Monolog;
 
 final class Utils
 {
-    const DEFAULT_JSON_FLAGS = JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE | JSON_PRESERVE_ZERO_FRACTION;
+    const DEFAULT_JSON_FLAGS = JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE | JSON_PRESERVE_ZERO_FRACTION | JSON_INVALID_UTF8_SUBSTITUTE;
 
     /**
      * @internal