Test on PHP8 env

.travis.yml

@@ -7,6 +7,7 @@ php:
   - 7.2
   - 7.3
   - 7.4
+  - nightly
 
 install:
   - composer update

composer.json

@@ -12,7 +12,7 @@
         "php": ">=5.6"
     },
     "require-dev": {
-        "phpunit/phpunit": "^5.7",
+        "phpunit/phpunit": "^5.7.27",
         "guzzlehttp/guzzle": "^6",
         "ext-json": "*"
     },

src/Exception/SyntaxError.php

@@ -4,7 +4,7 @@ namespace JsonMachine\Exception;
 
 class SyntaxError extends \RuntimeException
 {
-    public function __construct($message = "", $position)
+    public function __construct($message, $position)
     {
         parent::__construct($message." At position $position.");
     }