flag: update test case (fix build)

Change-Id: I2275dc703be4fda3feedf76483148eab853b43b8
Reviewed-on: https://go-review.googlesource.com/22360
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

src/flag/flag_test.go

@@ -393,7 +393,7 @@ const defaultOutput = `  -A	for bootstrapping, allow 'any' type
   -Z int
     	an int that defaults to zero
   -maxT timeout
-    	set timeout for dial
+    	set timeout for dial (default 0s)
 `
 
 func TestPrintDefaults(t *testing.T) {