Update map function documentation in the UI

[russorat]

The example from the Map function documentation needs to be updated to work with the new flux lib: https://v2.docs.influxdata.com/v2.0/reference/flux/functions/built-in/transformations/map/

[sanderson]

Ah, right. They removed the implicit column name mapping.

// This old syntax:
map(fn: (r) => r._value * r._value)

// Would get parsed as:
map(fn: (r) => ({ r._value: r._value * r._value }))

Flux doesn't do this any more, so the example function should be updated to use the 2nd form above.