TWEAK: Use proxy for bitcoinaverage.com.

[ghost]

Note: The motivation is that bitcoinaverage.com will soon be enforcing rate limits and charging. To prevent our users from needing their own accounts we have worked with bitcoinaverage.com to set up a load-bearing proxy.

[JustinDrake]

Is there a corresponding issue for openbazaar-go?

[coveralls]

Coverage decreased (-0.04%) to 52.838% when pulling 32d2273699b16eef52d6bc991c0eb85c88b7c337 on TS_ticker_proxy into 248b43c9783f7e8d34f2898a913c6f1172cfe72f on master.

[tyler-smith]

@JustinDrake Yeah it will need to be updated as well. I've created an issue for it https://github.com/OpenBazaar/openbazaar-go/issues/304