bug#25138: updated import error

[Robert Vollmert]

These days it’s:

Syntax error: unexpected token : (buildable (False)) (at line 471, column 4)
Syntax error: unexpected end of input

Relevant cabal extract:

   469  Executable          darcs
   470    if !flag(executable)
   471      buildable: False
   472    else
   473      buildable: True
   474