Replace deprecated TranslatorInterface (depends on Symfony 4.2) #123

As documented in UPGRADE-4.2.md. 
Minimum Symfony version raised from 3.4 to 4.2.
Explict dependency added for symfony/translation.

Controller/UploadController.php

@@ -8,7 +8,7 @@
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\HttpFoundation\File\UploadedFile;
 use Symfony\Component\HttpFoundation\StreamedResponse;
-use Symfony\Component\Translation\TranslatorInterface;
+use Symfony\Contracts\Translation\TranslatorInterface;
 
 use Symfony\Component\Finder\Finder;
 

composer.json

@@ -15,12 +15,13 @@
     "require": {
         "php": ">=7.1.3",
         "ext-gd": "*",
-        "symfony/http-foundation": "~3.4 || ~4.2 || ~5.0",
-        "symfony/form": "~3.4 || ~4.2 || ~5.0",
-        "symfony/validator": "~3.4 || ~4.2 || ~5.0",
-        "symfony/routing": "~3.4 || ~4.2 || ~5.0",
-        "symfony/config": "~3.4 || ~4.2 || ~5.0",
-        "symfony/twig-bridge": "~3.4 || ~4.2 || ~5.0",
+        "symfony/http-foundation": "~4.2 || ~5.0",
+        "symfony/form": "~4.2 || ~5.0",
+        "symfony/validator": "~4.2 || ~5.0",
+        "symfony/routing": "~4.2 || ~5.0",
+        "symfony/config": "~4.2 || ~5.0",
+        "symfony/translation": "~4.2 || ~5.0",
+        "symfony/twig-bridge": "~4.2 || ~5.0",
         "twig/twig": "^1.41 || ^2.10 || ~3.0",
         "twig/extensions": "~1.0",
         "friendsofsymfony/jsrouting-bundle": "@stable",