Laravel 5.6 updates

Travis config update

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

vendor/laravel/dusk/composer.json

@@ -10,17 +10,17 @@
         }
     ],
     "require": {
-        "php": ">=5.6.4",
-        "facebook/webdriver": "~1.0",
+        "php": ">=7.1.0",
+        "facebook/webdriver": "~1.3",
         "nesbot/carbon": "~1.20",
-        "illuminate/console": "~5.5",
-        "illuminate/support": "~5.5",
-        "symfony/console": "~3.2",
-        "symfony/process": "~3.2"
+        "illuminate/console": "~5.6",
+        "illuminate/support": "~5.6",
+        "symfony/console": "~4.0",
+        "symfony/process": "~4.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^5.7",
-        "mockery/mockery": "^0.9.6"
+        "mockery/mockery": "~1.0",
+        "phpunit/phpunit": "~7.0"
     },
     "autoload": {
         "psr-4": {
@@ -29,7 +29,7 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "2.0-dev"
+            "dev-master": "4.0-dev"
         },
         "laravel": {
             "providers": [