Update version number to 1.2.1

docs/console_config.md

 # PD Buddy Sink Serial Console Configuration Interface
 
-Version 1.2.0, 2018-01-13
+Version 1.2.1, 2018-05-28
 
 The PD Buddy Sink can be put into setup mode by holding the Setup button while
 plugging it into a computer.  In this mode, the device runs a configuration

src/usbcfg.c

 static const uint8_t vcom_string3[] = {
     USB_DESC_BYTE(12),                    /* bLength.                         */
     USB_DESC_BYTE(USB_DESCRIPTOR_STRING), /* bDescriptorType.                 */
-    '1', 0, '.', 0, '2', 0, '.', 0, '0', 0
+    '1', 0, '.', 0, '2', 0, '.', 0, '1', 0
 };
 
 /*