container start wrong error check

noticed that when checking for if the user has entered the escape sequence
after starting the container, the code was checking that the error from
inspect was a term.EscapeError rather than the error from attach in order to
mask the error returned to a nil one - I think this is the error that was
intended to be checked here.

Signed-off-by: Reed Allman <reed@rdallman.com>

cli/command/container/start.go

@@ -154,7 +154,7 @@ func runStart(dockerCli command.Cli, opts *startOptions) error {
 			}
 		}
 		if attachErr := <-cErr; attachErr != nil {
-			if _, ok := err.(term.EscapeError); ok {
+			if _, ok := attachErr.(term.EscapeError); ok {
 				// The user entered the detach escape sequence.
 				return nil
 			}