Updated note in format specification

[Alex Miller]

Several people have noticed over the years the note in the transit-format spec that says:

NOTE: Transit is a work in progress and may evolve based on feedback. As a result, while Transit is a great option for transferring data between applications, it should not yet be used for storing data durably over time. This recommendation will change when the specification is complete.

Transit was released as version 0.8 July 2014 and has not been changed since. As such, we have changed the note in the spec as follows:

NOTE: Transit is intended primarily as a wire protocol for transferring data between applications. If storing Transit data durably, readers and writers are expected to use the same version of Transit and you are responsible for migrating/transforming/re-storing that data when and if the transit format changes.