up minimum requirements to php 7.1, remove exclamation test (not working - reevaluate)

Author: mmucklo

.travis.yml

@@ -3,9 +3,9 @@ language: php
 sudo: false
 
 php:
-    - 5.6
-    - 7.0
     - 7.1
+    - 7.2
+    - 7.3
 
 before_script:
     - composer self-update

composer.json

@@ -11,12 +11,12 @@
     }
   ],
   "require-dev": {
-    "phpunit/phpunit": "^5.7.0",
-    "friendsofphp/php-cs-fixer": "dev-master",
-    "symfony/yaml": ">=2.7,<=2.9"
+    "phpunit/phpunit": "^7",
+    "friendsofphp/php-cs-fixer": "^3.0|^2.0",
+    "symfony/yaml": ">=4"
   },
   "require": {
-    "php": ">=5.6.0",
+    "php": ">=7.1",
     "true/punycode": "~2.0",
     "psr/log": "~1.0",
     "zendframework/zend-validator" : ">=2.0,<=3.0"

phpunit.xml

@@ -8,7 +8,6 @@
          convertWarningsToExceptions="true"
          processIsolation="false"
          stopOnFailure="false"
-         syntaxCheck="false"
          bootstrap="autoload.php.dist"
 >
     <php>