The documentation for %v behavior for compound objects uses an ellipsis
to indicate indefinite lenght of elements. This is done for struct
fields as well as elements of arrays and slices. This adds the missing
ellipsis for maps.

Change-Id: Ia433387fe189d2daf5095df32085a541458f00a1
Reviewed-on: https://go-review.googlesource.com/107623Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>