Adding sed compatibility for MacOS (#520)

Author: Maleware

template/default.nix

@@ -114,6 +114,10 @@ rec {
     # (see https://github.com/pre-commit/pre-commit-hooks?tab=readme-ov-file#trailing-whitespace).
     # So, remove the trailing newline already here to avoid that an
     # unnecessary change is shown in Git.
-    sed -i '$d' Cargo.nix
+    if [[ "$(uname)" == "Darwin" ]]; then
+      sed -i \"\" '$d' Cargo.nix
+    else
+      sed -i '$d' Cargo.nix
+    fi
   '';
 }