Merge pull request #4573 from laravel/defaults-55

[5.5] Use composer platform config

composer.json

@@ -5,7 +5,7 @@
     "license": "MIT",
     "type": "project",
     "require": {
-        "php": ">=7.0.0",
+        "php": "^7.0.0",
         "fideloper/proxy": "~3.3",
         "laravel/framework": "5.5.*",
         "laravel/tinker": "~1.0"
@@ -15,7 +15,7 @@
         "fzaninotto/faker": "~1.4",
         "mockery/mockery": "~1.0",
         "phpunit/phpunit": "~6.0",
-        "symfony/thanks": "^1.0"
+        "symfony/thanks": "~1.0"
     },
     "autoload": {
         "classmap": [
@@ -50,6 +50,9 @@
         ]
     },
     "config": {
+        "platform": {
+            "php": "7.0.0"
+        },
         "preferred-install": "dist",
         "sort-packages": true,
         "optimize-autoloader": true