fmt: remove extra space in doc for compound objects

Fixes #15339

Change-Id: I0b006deefb58ccfc47beae4e1b8da3d77fafda6b
Reviewed-on: https://go-review.googlesource.com/22148Reviewed-by: Rob Pike <r@golang.org>

src/fmt/doc.go

@@ -62,7 +62,7 @@
 	For compound objects, the elements are printed using these rules, recursively,
 	laid out like this:
 		struct:             {field0 field1 ...}
-		array, slice:       [elem0  elem1 ...]
+		array, slice:       [elem0 elem1 ...]
 		maps:               map[key1:value1 key2:value2]
 		pointer to above:   &{}, &[], &map[]