doc: Fix type in Hooking up the JTAG Adapter

We are talking about adapter connectivity in this chapter. It should
be "dongles" instead of "cables".

Change-Id: I7bd4307765517375caa2af86dfc929d0ef66c3e6
Signed-off-by: Yasushi SHOJI <yashi@spacecubics.com>
Reviewed-on: http://openocd.zylin.com/6040
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins

doc/openocd.texi

@@ -834,7 +834,7 @@ using Eclipse or some other GUI.
 Today's most common case is a dongle with a JTAG cable on one side
 (such as a ribbon cable with a 10-pin or 20-pin IDC connector)
 and a USB cable on the other.
-Instead of USB, some cables use Ethernet;
+Instead of USB, some dongles use Ethernet;
 older ones may use a PC parallel port, or even a serial port.
 
 @enumerate