fix wrong spells in config.go

Signed-off-by: czm <zhongming.chang@daocloud.io>

dfget/config/config.go

@@ -372,7 +372,7 @@ type RuntimeVariable struct {
 
 	// ServerAliveTime specify the alive duration for which
 	// uploader keeps no accessing by any uploading requests.
-	// After this period, the uploader will automically exit.
+	// After this period, the uploader will automatically exit.
 	ServerAliveTime time.Duration
 }