Laravel 5.6 updates

Travis config update

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

vendor/phpunit/php-code-coverage/composer.json

@@ -25,22 +25,22 @@
     },
     "prefer-stable": true,
     "require": {
-        "php": "^7.0",
+        "php": "^7.1",
         "ext-dom": "*",
         "ext-xmlwriter": "*",
-        "phpunit/php-file-iterator": "^1.4.2",
-        "phpunit/php-token-stream": "^2.0.1",
+        "phpunit/php-file-iterator": "^2.0",
+        "phpunit/php-token-stream": "^3.0",
         "phpunit/php-text-template": "^1.2.1",
         "sebastian/code-unit-reverse-lookup": "^1.0.1",
-        "sebastian/environment": "^3.0",
+        "sebastian/environment": "^3.1",
         "sebastian/version": "^2.0.1",
         "theseer/tokenizer": "^1.1"
     },
     "require-dev": {
-        "phpunit/phpunit": "^6.0"
+        "phpunit/phpunit": "^7.0"
     },
     "suggest": {
-        "ext-xdebug": "^2.5.5"
+        "ext-xdebug": "^2.6.0"
     },
     "autoload": {
         "classmap": [
@@ -49,7 +49,7 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "5.3.x-dev"
+            "dev-master": "6.0-dev"
         }
     }
 }