change log_dir flag to logdir

change log_dir flag to logdir

weed/glog/glog.go

@@ -46,7 +46,7 @@
 //	-stderrthreshold=ERROR
 //		Log events at or above this severity are logged to standard
 //		error as well as to files.
-//	-log_dir=""
+//	-logdir=""
 //		Log files will be written to this directory instead of the
 //		default temporary directory.
 //