fixing laravel-5.5 build

Author: ArturMoczulski

src/RollbarServiceProvider.php

@@ -48,7 +48,7 @@ public function boot()
                 }
 
                 try {
-                    $result = $app[get_class(RollbarLogHandler)]->log($level, $message, $context);
+                    $result = $app[RollbarLogHandler::class]->log($level, $message, $context);
                 } catch (BelowParseLevelException $exception) {
                     return;
                 }