Make Translator compatible with Laravel 6

It's contract will change in Laravel 6. We extend from Symfony's
translator, but need to be compatible with that from Laravel in
order to use its validation package.

References:
- https://laravel.com/docs/6.x/upgrade#trans-and-trans-choice
- 8557dc56b1 (diff-88bc04a1548d09aa6250d902d1ac2b4c)

framework/core/src/Locale/Translator.php

@@ -17,6 +17,16 @@ class Translator extends BaseTranslator implements TranslatorContract
 {
     const REFERENCE_REGEX = '/^=>\s*([a-z0-9_\-\.]+)$/i';
 
+    public function get($key, array $replace = [], $locale = null)
+    {
+        return $this->trans($key, $replace, null, $locale);
+    }
+
+    public function choice($key, $number, array $replace = [], $locale = null)
+    {
+        return $this->transChoice($key, $number, $replace, nil, $locale);
+    }
+
     /**
      * {@inheritdoc}
      */