Correction to api_mission

The first value of the array seems to actually indicate the current status of the expedition (0 for not on expedition, 1 for on expedition, 2 for completed expedition), not page (whatever that means?).

I did a bit of double checking and this [Japanese site](http://blog.livedoor.jp/ymk_kc/archives/3334665.html) seems to agree, though it doesn't mention that the value can be a 2.