bumped min version to 7.1

composer.json

@@ -5,7 +5,7 @@
     "description": "Project description",
     "minimum-stability": "dev",
     "require": {
-        "php": "^7.0",
+        "php": "^7.1",
         "symfony/flex": "1.0.x-dev",
         "symfony/framework-bundle": "3.3.x-dev",
         "symfony/yaml": "3.3.x-dev"
@@ -15,7 +15,7 @@
     },
     "config": {
         "platform": {
-            "php": "7.0"
+            "php": "7.1"
         },
         "preferred-install": {
             "*": "dist"