treewide: "does not exists" -> "does not exist"

I noticed this minor grammar mistake when running update.nix, and then
while grepping to find the source I noticed we had it a few times in
Nixpkgs.  Just as easy to fix treewide as it was to fix the one
occurrence I noticed.

1 files changed, 2 insertions, 2 deletions

diff --git a/maintainers/scripts/update.nix b/maintainers/scripts/update.nix
index 7435cf64425..d881d68301b 100755
--- a/maintainers/scripts/update.nix
+++ b/maintainers/scripts/update.nix
@@ -103,7 +103,7 @@ let
       pathContent = lib.attrByPath prefix null pkgs;
     in
       if pathContent == null then
-        builtins.throw "Attribute path `${path}` does not exists."
+        builtins.throw "Attribute path `${path}` does not exist."
       else
         packagesWithPath prefix (path: pkg: builtins.hasAttr "updateScript" pkg)
                        pathContent;
@@ -115,7 +115,7 @@ let
         package = lib.attrByPath (lib.splitString "." path) null pkgs;
     in
       if package == null then
-        builtins.throw "Package with an attribute name `${path}` does not exists."
+        builtins.throw "Package with an attribute name `${path}` does not exist."
       else if ! builtins.hasAttr "updateScript" package then
         builtins.throw "Package with an attribute name `${path}` does not have a `passthru.updateScript` attribute defined."
       else