fmt: make %v doc for compound objects consistent

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>

src/fmt/doc.go

@@ -64,7 +64,7 @@
 	laid out like this:
 		struct:             {field0 field1 ...}
 		array, slice:       [elem0 elem1 ...]
-		maps:               map[key1:value1 key2:value2]
+		maps:               map[key1:value1 key2:value2 ...]
 		pointer to above:   &{}, &[], &map[]
 
 	Width is specified by an optional decimal number immediately preceding the verb.