Require php 7.1, upgrade dependencies and require Symfony 4 (php-pm#449)

Author: andig

.travis.yml

@@ -3,7 +3,6 @@ sudo: false
 language: php
 
 php:
-  - 7.0
   - 7.1
   - 7.2
   - 7.3
@@ -66,7 +65,7 @@ matrix:
 jobs:
   include:
     - stage: lint
-      php: 7.1
+      php: 7.3
       install:
         - rm -f ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/xdebug.ini
         - composer require "phpstan/phpstan" "friendsofphp/php-cs-fixer:^2.8"

composer.json

@@ -3,22 +3,22 @@
     "description": "PHP-PM is a process manager, supercharger and load balancer for PHP applications.",
     "license": "MIT",
     "require": {
-        "php": "^7.0",
-        "symfony/console": "^2.6|^3.0|^4.0",
-        "symfony/debug": "^2.6|^3.0|^4.0",
-        "symfony/process": "^2.6|^3.0|^4.0",
+        "php": "^7.1",
+        "symfony/console": "^3.4|^4",
+        "symfony/debug": "^3.4|^4",
+        "symfony/process": "^3.4|^4",
         "react/event-loop": "^1.0",
         "react/http": "^0.8",
         "react/stream": "^1.0",
         "react/socket": "^1.0",
-        "react/child-process": "^0.5",
+        "react/child-process": "^0.6",
         "monolog/monolog": "^1.3",
         "psr/http-server-handler": "^1.0",
         "ringcentral/psr7": "^1.2"
     },
     "require-dev": {
         "mockery/mockery": "^1.0",
-        "phpunit/phpunit": "^5.7"
+        "phpunit/phpunit": "^7.0"
     },
     "autoload": {
         "psr-4": {