Laravel 5.6 updates

Travis config update

Removed HHVM script as Laravel no longer support HHVM after releasing 5.3

vendor/symfony/debug/composer.json

@@ -16,14 +16,14 @@
         }
     ],
     "require": {
-        "php": "^5.5.9|>=7.0.8",
+        "php": "^7.1.3",
         "psr/log": "~1.0"
     },
     "conflict": {
-        "symfony/http-kernel": ">=2.3,<2.3.24|~2.4.0|>=2.5,<2.5.9|>=2.6,<2.6.2"
+        "symfony/http-kernel": "<3.4"
     },
     "require-dev": {
-        "symfony/http-kernel": "~2.8|~3.0|~4.0"
+        "symfony/http-kernel": "~3.4|~4.0"
     },
     "autoload": {
         "psr-4": { "Symfony\\Component\\Debug\\": "" },
@@ -34,7 +34,7 @@
     "minimum-stability": "dev",
     "extra": {
         "branch-alias": {
-            "dev-master": "3.4-dev"
+            "dev-master": "4.1-dev"
         }
     }
 }