docs: fix a typo in registry_mirror.md
@@ -38,7 +38,7 @@ For example, if your mirror is serving on `http://10.0.0.2:5000`, you would run:
**NOTE:**
Depending on your local host setup, you may be able to add the
`--registry-mirror` options to the `DOCKER_OPTS` variable in
-`/etc/defaults/docker`.
+`/etc/default/docker`.
### Step 2: Run the local registry mirror