Minor syntactic changes

Hi folks,

This is an awesome project, can't believe I only stumbled upon it now - definitely will be talking to the rest of our dev team about it as we could make use of it.

I wanted to familiarise myself with the JavaScript code before getting my hands dirty with some data visualisation. I had a look at [CONTRIBUTING.md](https://github.com/twitter/zipkin/blob/master/CONTRIBUTING.md) for guidelines but those are just for Scala, hence I went by what seemed to be the convention throughout the code base and made the following changes:
- Added a few missing semicolons
- Removed a repeated variable definition
- Used strict equality where applicable

I hope you find these changes useful - if you feel like they won't be adding any value then please feel free to close this pull request.

Cheers,

Andreas