Added phpstan, phpunit, php-cs-fixer into require-dev

composer.json

 {
     "name": "silex/silex",
     "description": "The PHP micro-framework based on the Symfony Components",
-    "keywords": ["microframework"],
+    "keywords": [ "microframework" ],
     "homepage": "https://silex.symfony.com",
     "license": "MIT",
     "authors": [
@@ -12,6 +12,10 @@
         {
             "name": "Igor Wiedler",
             "email": "igor@wiedler.ch"
+        },
+        {
+            "name": "David Weston",
+            "email": "westie@typefish.co.uk"
         }
     ],
     "require": {
@@ -23,46 +27,56 @@
         "symfony/routing": "^4.0"
     },
     "require-dev": {
+        "doctrine/dbal": "^2.2",
+        "friendsofphp/php-cs-fixer": "^2.13",
+        "monolog/monolog": "^1.4.1",
+        "phpstan/phpstan": "^0.10.3",
+        "phpunit/phpunit": "^7.4",
+        "swiftmailer/swiftmailer": "^5",
         "symfony/asset": "^4.0",
-        "symfony/expression-language": "^4.0",
-        "symfony/security": "^4.0",
-        "symfony/config": "^4.0",
-        "symfony/form": "^4.0",
         "symfony/browser-kit": "^4.0",
+        "symfony/config": "^4.0",
         "symfony/css-selector": "^4.0",
         "symfony/debug": "^4.0",
+        "symfony/doctrine-bridge": "^4.0",
         "symfony/dom-crawler": "^4.0",
+        "symfony/expression-language": "^4.0",
         "symfony/finder": "^4.0",
+        "symfony/form": "^4.0",
         "symfony/intl": "^4.0",
         "symfony/monolog-bridge": "^4.0",
-        "symfony/doctrine-bridge": "^4.0",
         "symfony/options-resolver": "^4.0",
         "symfony/phpunit-bridge": "^3.2",
         "symfony/process": "^4.0",
+        "symfony/security": "^4.0",
         "symfony/serializer": "^4.0",
         "symfony/translation": "^4.0",
         "symfony/twig-bridge": "^4.0",
         "symfony/validator": "^4.0",
         "symfony/var-dumper": "^4.0",
-        "twig/twig": "^2.0",
-        "doctrine/dbal": "^2.2",
-        "swiftmailer/swiftmailer": "^5",
-        "monolog/monolog": "^1.4.1",
-        "symfony/web-link": "^4.0"
+        "symfony/web-link": "^4.0",
+        "twig/twig": "^2.0"
     },
     "replace": {
         "silex/api": "self.version",
         "silex/providers": "self.version"
     },
     "autoload": {
-        "psr-4": { "Silex\\": "src/Silex" }
+        "psr-4": {
+            "Silex\\": "src/Silex"
+        }
     },
-    "autoload-dev" : {
-        "psr-4": { "Silex\\Tests\\" : "tests/Silex/Tests" }
+    "autoload-dev": {
+        "psr-4": {
+            "Silex\\Tests\\": "tests/Silex/Tests"
+        }
     },
     "extra": {
         "branch-alias": {
             "dev-master": "2.3.x-dev"
         }
+    },
+    "config": {
+        "sort-packages": true
     }
 }