[minor] Documentation: tables exist in all regions now

[batpad]

Just wondering if this line in the comments is no longer true: https://github.com/mapbox/streambot/blob/master/cloudformation/streambot.template.js#L9

Since it seems that the Dynamo tables now exist in all regions as per https://github.com/mapbox/streambot/commit/0a579dae0c672564623641d04cc3afa5f3ca50ce

cc @rclark

[rclark]

:wave: yeah this line and also some wording in the readme are outdated.