Mapping Block now function documentation should say RFC 7231 not ISO 8601

[lukestanley]

Bug description
The documentation says the "now" function from the mapping block "Returns the current UTC timestamp in ISO 8601 format." which is not true. Since it uses new Date().toUTCString() we can expect it to output a UTC timestamp in RFC 7231 format according to MDN.

Reproduction steps
See https://kendraio-app.readthedocs.io/en/latest/workflow/blocks/mapping.html#now
Note that it says "ISO 8601 format".
Go to the source for now: https://raw.githubusercontent.com/kendraio/kendraio-app/develop/src/app/blocks/mapping-block/mapping-util.ts and note that it uses new Date().toUTCString().
Check the expected output format of toUTCString on MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toUTCString)
Note that toUTCString uses RFC 7231.

Expected behaviour
We'll need the docs to correctly say RFC 7231.

Additional context
This problem was noticed when trying to parse the results of now(), and getting failures due to it not being the right format. This blocks Donald.