remove the invalid rule from the go syntax file

Remove the `invalid` rule from the golang syntax highlighting file. It would display an highlighted error rectangle if a line ended in whitespace. This had a lot of false positives though, in that it would mark a line as an error as you were typing, before you typed the first non-ws char. It's a bit annoying for this to happen for every line you type.

![screen shot 2014-06-28 at 10 24 06 pm](https://cloud.githubusercontent.com/assets/1269969/3422582/fb8ee8c8-ff4d-11e3-8af8-e8d6c5862a4c.png)