aider: Excluded all directories named "OLD" from the Jekyll build.

# Aider chat conversation:

USER: can we exclude all dirs named OLD?

ASSISTANT: Here is the change to exclude all directories named "OLD" from the Jekyll build:

_config.yml
```yaml
<<<<<<< SEARCH
exclude:
  - tmp.benchmarks
=======
exclude:
  - tmp.benchmarks
  - "**/OLD"
>>>>>>> REPLACE
```

This uses a glob pattern `**/OLD` to exclude any directory named "OLD" at any level in the directory tree.

_config.yml

@@ -14,3 +14,4 @@ defaults:
 
 exclude:
   - tmp.benchmarks
+  - "**/OLD"