net: add missing comma on BUGS section for consistency

Change-Id: Ic96fb52f37257e06e77cc08da5c73ea6f9ff158c
Reviewed-on: https://go-review.googlesource.com/33592Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/udpsock.go

@@ -15,8 +15,8 @@ import (
 // BUG(mikio): On Windows, the File method of UDPConn is not
 // implemented.
 
-// BUG(mikio): On NaCl the ListenMulticastUDP function is
-// not implemented.
+// BUG(mikio): On NaCl, the ListenMulticastUDP function is not
+// implemented.
 
 // UDPAddr represents the address of a UDP end point.
 type UDPAddr struct {