Logging in fails intermittently

As originally reported by [Ryan Whitney on Twitter](https://twitter.com/ryanwhitney/status/426487497015586816), logging in is failing intermittently:

```
/home/todd/.rbenv/versions/1.9.3-p194/gemsets/mint-exporter/gems/wait-0.5.1/lib/wait.rb:136:in `until': Wait::ResultInvalid (Wait::ResultInvalid)
	from /home/todd/code/mint-exporter/lib/mint_exporter.rb:39:in `log_in'
	from /home/todd/code/mint-exporter/lib/mint_exporter.rb:15:in `initialize'
	from mint-exporter.rb:15:in `new'
	from mint-exporter.rb:15:in `<main>'
```