cmd/benchcmp: close file when parse done

prevent file descriptor leak

Signed-off-by: Tw <tw19881113@gmail.com>

Change-Id: Ia1cacb3a287477b1f9b50fae248b5c34156c9557
Reviewed-on: https://go-review.googlesource.com/2740
Reviewed-by: Rob Pike <r@golang.org>

cmd/benchcmp/benchcmp.go

@@ -142,6 +142,7 @@ func parseFile(path string) parse.BenchSet {
 	if err != nil {
 		fatal(err)
 	}
+	defer f.Close()
 	bb, err := parse.ParseBenchSet(f)
 	if err != nil {
 		fatal(err)