In docs, move commas out of code

The commas separating these three keywords are not code themselves – not what the user would write – so they should be outside of the `<tt>` tags.

Edits the table in the section [Operators and Aliases](http://coffeescript.org/#operators).

Before:

![portion of the operators table before my change](https://f.cloud.github.com/assets/79168/2026104/7bb34a3a-8889-11e3-8d2a-cda58a194f28.png)

After:

![portion of the operators table after my change](https://f.cloud.github.com/assets/79168/2026105/85a6ddc2-8889-11e3-9fbe-a3a51b30c791.png)