Upgrade Alpaca SDK Version

This release upgrades the version of the Alpaca SDK, a major dependency for pylivetrader's Alpaca backend. Due to the update to the websockets library, this means that support for Python 3.5 is ended. As of this version, the only supported version is Python 3.6. The lack of explicit support for Python 3.7 at the moment is due to a compatibility issue with some of the Zipline dependencies when building. We'll continue exploring options to restore Python 3.7 support, but for now, Python 3.6 is the recommended version for Pylivetrader.

Additionally, a fix was made to the handling of timestamps such that they should now once again work with Pipeline live's USEquityPricing. A fix was also made to smoke test to support algorithms using the all_orders method.