Update nano to 4.3

Release notes at https://nano-editor.org/news.php

2019.06.18 - GNU nano 4.3
* The ability to read from and write to a FIFO has been regained.
* Startup time is reduced by fully parsing a syntax only when needed.
* Asking for help (^G) when using --operatingdir does not crash.
* The reading of a huge or slow file can be stopped with ^C.
* Cut, zap, and copy operations are undone separately when intermixed.
* M-D reports the correct number of lines (zero for an empty buffer).

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>