Laravel 5.6 updates

Travis config update

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

vendor/laravel/framework/src/Illuminate/Database/DatabaseManager.php

@@ -137,7 +137,7 @@ class DatabaseManager implements ConnectionResolverInterface
         $connections = $this->app['config']['database.connections'];
 
         if (is_null($config = Arr::get($connections, $name))) {
-            throw new InvalidArgumentException("Database [$name] not configured.");
+            throw new InvalidArgumentException("Database [{$name}] not configured.");
         }
 
         return $config;