[Nauty] two small problems with nauty version 2.8.6

[Brendan McKay]

Dear nauty people,

Gonne Kretschmer reported that gentreeg and gentourng give
the wrong output for 2 vertices.  Other sizes seem ok.  I won't
be releasing a new version right away but if these bugs are an
issue for you, you can fetch corrected programs here:

https://users.cecs.anu.edu.au/~bdm/nauty/gentreeg.c
https://users.cecs.anu.edu.au/~bdm/nauty/gentourng.c

Cheers, Brendan.