bibtool: 2.67 -> 2.68

cf. https://github.com/ge-ne/bibtool/issues/76

pkgs/tools/misc/bibtool/default.nix

@@ -2,11 +2,11 @@
 
 stdenv.mkDerivation rec {
   pname = "bibtool";
-  version = "2.67";
+  version = "2.68";
 
   src = fetchurl {
     url = "http://www.gerd-neugebauer.de/software/TeX/BibTool/BibTool-${version}.tar.gz";
-    sha256 = "116pv532mz0q954y5b7c6zipnamc05f0x7g5x1b674jsjxh42v2v";
+    sha256 = "1ymq901ckaysq2n1bplk1064rb2njq9n30pii15w157y0lxcwd3i";
   };
 
   # Perl for running test suite.
@@ -15,6 +15,7 @@ stdenv.mkDerivation rec {
   installTargets = [ "install" "install.man" ];
 
   doCheck = true;
+  checkTarget = "test";
 
   meta = with stdenv.lib; {
     description = "Tool for manipulating BibTeX bibliographies";