Rotate bike_id on free_bike_status (#147)

Breaking change --v2.0-RC

* Rotate bike_id on free_bike_status
* rotate id after each trip "at minimum"

gbfs.md

@@ -298,7 +298,7 @@ Describes bikes that are not at a station and are not currently in the middle of
 Field Name                       | Required  | Type            | Defines
 -------------------------------- | ----------| --------------- | ---------------------
 _`bikes`_                        | Yes       | Array           | Array that contains one object per bike that is currently stopped as defined below.
-\- `bike_id`                | Yes       | ID              | Identifier of a bike.
+\- `bike_id`                | Yes       | ID              | Identifier of a bike. *Beta (v2.0-RC):* Identifier of a bike, rotated to a random string, at minimum, after each trip to protect privacy. Note: Persistent bike_id, published publicly, could pose a threat to individual traveler privacy.
 \- `lat`                    | Yes       | Latitude        | Latitude of the bike.
 \- `lon`                    | Yes       | Longitude       | Longitude of the bike.
 \-&nbsp;`is_reserved`            | Yes       | Boolean         | Is the bike currently reserved? <br /><br /> `1` - Bike is currently reserved. <br /> `0` - Bike is not currently reserved.