Switch to new OSM OAuth app for dev

The old one was called gittip-test. I can't find where it is! It's not under the vendors@gratipay.com account, nor my personal account. O.O

Fixes a regression from https://github.com/gratipay/inside.gratipay.com/issues/73.

![5a85222c-5609-11e4-8c51-c32d804a2402](https://cloud.githubusercontent.com/assets/134455/4681010/84758328-560f-11e4-9e4b-37d7c12a2283.png)