Post-release version bump

There will be a version 1.2 eventually, hopefully bringing support for
some new PDO(s).

docs/console_config.md

 # PD Buddy Sink Serial Console Configuration Interface
 
-Version 1.1.0, 2017-08-02
+Version 1.2.0-dev, 2017-09-09
 
 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

  * Serial Number string.
  */
 static const uint8_t vcom_string3[] = {
-    USB_DESC_BYTE(12),                    /* bLength.                         */
+    USB_DESC_BYTE(20),                    /* bLength.                         */
     USB_DESC_BYTE(USB_DESCRIPTOR_STRING), /* bDescriptorType.                 */
-    '1', 0, '.', 0, '1', 0, '.', 0, '0', 0
+    '1', 0, '.', 0, '2', 0, '.', 0, '0', 0, '-', 0, 'd', 0, 'e', 0, 'v', 0
 };
 
 /*