keybase: buildFlags -> tags

pkgs/tools/security/keybase/default.nix

···
   ];
 
   buildInputs = lib.optionals stdenv.isDarwin [ AVFoundation AudioToolbox ImageIO CoreMedia Foundation CoreGraphics MediaToolbox ];
-  buildFlags = [ "-tags production" ];
+  tags = [ "production" ];
 
   meta = with lib; {
     homepage = "https://www.keybase.io/";