--path_prefix startup URL omits trailing slash

When I execute `tensorboard --logdir storage/logs --path_prefix /test`, I get this message: ```TensorBoard 1.8.0 at http://lcswillems-ubuntu:6006/test (Press CTRL+C to quit)```. But when I click on the link, I get `Not found` page.

I precise that when I execute `tensorboard --logdir storage/logs`, it is working.

I use Tensorboard 1.8.0.