Updated minimal PHP version to 7.1.

Author: corpsee

composer.json

@@ -30,9 +30,9 @@
         }
     },
     "require": {
-        "php":              ">=5.6.0",
-        "nikic/php-parser": "3.*",
-        "symfony/console":  "~3.4.0"
+        "php":              ">=7.1.0",
+        "nikic/php-parser": "^4.2",
+        "symfony/console":  "^4.3"
     },
     "bin": [
         "bin/phpdoc-checker"