Fix bash syntax in rrd doc.

doc/rrd-howto.txt

@@ -5,7 +5,7 @@ touch rrd
 rrdtool create vlc.rrd --step 1 "DS:in:GAUGE:10:0:30000" "DS:demux:GAUGE:10:0:30000" "DS:out:GAUGE:10:0:30000" "RRA:AVERAGE:0,5:1:86400"
 
 # Start "listening" the RRD file
-tail -f rrd |while read in;do;echo $in;rrdtool update vlc.rrd `echo $in`;done
+tail -f rrd |while read in;do echo $in;rrdtool update vlc.rrd `echo $in`;done
 
 # Start vlc
 vlc normal_vlc_stuff --extraintf logger --rrd-file rrd