Replace flag.Int with flag.Duration to represent time

This makes it less error prune, more readable and easier to use since
it does'nt require doing math convertions by hand in order to get time
in seconds.

Signed-off-by: Wagner Riffel <wgrriffel@gmail.com>

main.go

@@ -13,7 +13,7 @@ import (
 )
 
 var (
-	timer = flag.Int64("timer", 3600, "This parameter define time in seconds to verify API ")
+	timer = flag.Duration("timer", time.Hour, "This parameter define time to verify API ")
 )
 
 // LastValues ...
@@ -102,7 +102,7 @@ func routine(duration time.Duration) {
 			lastValues = *currentValue
 		}
 		fmt.Println("opa time? ", duration, *timer)
-		time.Sleep(duration * time.Second)
+		time.Sleep(duration)
 	}
 }