adns: use title case for `meta.description`

pkgs/by-name/ad/adns/package.nix

···
 
   meta = {
     homepage = "http://www.chiark.greenend.org.uk/~ian/adns/";
-    description = "Asynchronous DNS Resolver Library";
+    description = "Asynchronous DNS resolver library";
     license = [
       lib.licenses.gpl3Plus