Composer updates (#165)

* updated composer dependencies
* updated README about composer install

composer.json

@@ -13,6 +13,7 @@
         "sensio/framework-extra-bundle": "^5.1",
         "symfony/asset": "^4.0",
         "symfony/console": "^4.0",
+        "symfony/dotenv": "^4.0",
         "symfony/expression-language": "^4.0",
         "symfony/flex": "^1.0",
         "symfony/form": "^4.0",
@@ -42,7 +43,6 @@
         "symfony/browser-kit": "^4.0",
         "symfony/css-selector": "^4.0",
         "symfony/debug-pack": "^1.0",
-        "symfony/dotenv": "^4.0",
         "symfony/maker-bundle": "^1.0",
         "symfony/phpunit-bridge": "^4.0",
         "symfony/web-server-bundle": "^4.0"