cmd/addr2line: defer closing objfile

Change-Id: I19ff9d231c4cc779b0737802c3c40ee2e00934dd
Reviewed-on: https://go-review.googlesource.com/c/147477Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/addr2line/main.go

@@ -61,6 +61,7 @@ func main() {
 	if err != nil {
 		log.Fatal(err)
 	}
+	defer f.Close()
 
 	tab, err := f.PCLineTable()
 	if err != nil {