content: update code in imports example

The important bit in this slide is the factored imports, and
the code example needs a reason to import two packages.

The `math.Sqrt` function is less likely to distract the reader
from the point than the `math.Nextafter`, which many people
are not familiar with.

Fixes golang/go#13180

Change-Id: Ibb746312b1a3ecbaed79ad3a83ad2f5acf0237ba
Reviewed-by: Andrew Gerrand <>
1 file changed