Log Message:
Update to nabud-1.2.1.  Upstream changes:

### nabud-1.2.1
* Experimental support for Cygwin (64-bit).
* Support command history / editing in nabuctl in Docker builds,
  plus some additional Docker fixes.  From Christopher Masto.
* Added a FlowControl property to Connection objects.  This allows users
  who have modified their NABU HCCA port to support RTS/CTS flow control
  to enable it.
* nabuctl now displays the serial connection properties (baud rate,
  stop bits, and flow control) when viewing connection details.
* nabuctl now displays the file that the NABU will receive as the default
  boot image (image 000001) even if this is not specified in the config
  file or selected with nabuctl.  Suggested by jefferystone on Discord.