The example plugin not loading on Safari

Hi Tensorboard team,

After built the example plugin (https://github.com/tensorflow/tensorboard/tree/master/tensorboard/examples/plugins/example_raw_scalars), I found it can't be loaded on Safari. However, it does work on Chrome. The error message shows like this:

W1117 22:38:41.826974 13009694720 application.py:558] path /data/static/index.js not found, sending 404

Apparently it's a path issue. When I click the plugin tag on Safari, it's requesting to the wrong path. After changing this line from

es_module_path="/static/index.js"

to

es_module_path="/plugin/example_raw_scalars/static/index.js"

it works on Safari but doesn't work on Chrome because of the extra path.

I guess this issue is caused by this line of code:

module_json = json.dumps("." + module_path)

Where relative path behaves differently on Apple Webkit & Chromium. Is this a bug? Thanks.

Reproduce the example_raw_scalars plugin loading issue in Safari and Chrome. Inspect tensorboard/examples/plugins/example_raw_scalars/tensorboard_plugin_example_raw_scalars/plugin.py at line 108 and tensorboard/backend/application.py at line 376, then trace the generated module path. Done means the example plugin loads correctly in both browsers without a 404 for index.js.