auctex: fix build

prior to this change, the build fails because the documentation cannot be
generated due to a missing latex package (probably fallout from a texlive
update):

! LaTeX Error: File `hypdoc.sty' not found.

Type X to quit or <RETURN> to proceed,
or enter new name. (Default extension: sty)

Enter file name:
! Emergency stop.
<read *>

l.29  \begin{document}
                      ^^M
!  ==> Fatal error occurred, no output PDF file produced!
Transcript written on preview.log.
make[1]: *** [Makefile:91: preview.pdf] Error 1
make[1]: Leaving directory '/build/auctex-12.3/latex'
make: *** [Makefile:219: texmf] Error 2

pkgs/tools/typesetting/tex/auctex/default.nix

@@ -17,7 +17,7 @@ let auctex = stdenv.mkDerivation ( rec {
   buildInputs = [
     emacs
     ghostscript
-    texlive.combined.scheme-basic
+    (texlive.combine { inherit (texlive) scheme-basic hypdoc;  })
   ];
 
   preConfigure = ''