xkbvalidate: Rename output binary to xkbvalidate

So far, the output binary has been just "validate", which is quite a
very generic name and doesn't match the package name.

Even though I highly doubt that this program will ever be used outside
of NixOS modules, it's nevertheless less confusing to have a consistent
naming.

Signed-off-by: aszlig <[e-mail]>

nixos/modules/services/x11/xserver.nix

···
       nativeBuildInputs = [ pkgs.xkbvalidate ];
       preferLocalBuild = true;
     } ''
-      validate "$xkbModel" "$layout" "$xkbVariant" "$xkbOptions"
+      xkbvalidate "$xkbModel" "$layout" "$xkbVariant" "$xkbOptions"
       touch "$out"
     '');
 

pkgs/tools/X11/xkbvalidate/default.nix

···
 } ''
   mkdir -p "$out/bin"
   $CC -std=c11 -Wall -pedantic -lxkbcommon ${./xkbvalidate.c} \
-    -o "$out/bin/validate"
+    -o "$out/bin/xkbvalidate"
 ''