Laravel 5.6 updates

Travis config update

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

vendor/phpunit/php-token-stream/composer.json

@@ -14,12 +14,13 @@
     "support": {
         "issues": "https://github.com/sebastianbergmann/php-token-stream/issues"
     },
+    "prefer-stable": true,
     "require": {
-        "php": "^7.0",
+        "php": "^7.1",
         "ext-tokenizer": "*"
     },
     "require-dev": {
-        "phpunit/phpunit": "^6.2.4"
+        "phpunit/phpunit": "^7.0"
     },
     "config": {
         "optimize-autoloader": true,
@@ -32,7 +33,7 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "2.0-dev"
+            "dev-master": "3.0-dev"
         }
     }
 }