better specify Fernet version

[chadwhitacre]

The cryptography docs link to the master branch of the Fernet spec, which is a mutable resource, a moving target. The version number advertised by Fernet on the current master, 0x80, is ambiguous. The cryptography source gives no direct indication as to what version it implements.

What precise version of Fernet does cryptography implement?

[alex]

Cryptography implements the only version of fernet that exists in real life. Though you've noted that in theory some ambigiuty exists, in reality I have never seen any confusion about this, and all the fernet libraries in various langauges implement the same standard.