Use OS specific path separator

[kumaranvpl]

In the web_component.py file, an os specific path is constructed at line 33 using os.path.join.

But immediately the path is checked whether it starts with "/" or not. "/" is a linux specific path separator and ideally the code should use os specific path separator.

This PR fixes that issue.

Because of this issue, in windows, full_path \some\dir\file.js becomes /\some\dir\file.js and later when converted to a URL it becomes http://host:port//some/dir/file.js which is not really a valid URL.

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[wwwillchen]

thanks!

[kumaranvpl]

thanks!

@wwwillchen No problem. Happy to contribute.