go/ast: Fix typo for the godoc of ObjKind
go/ast: Fix typo for the godoc of ObjKind

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/7232045

Committer: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang