docs: add missing `

Author: roucc

CONTRIBUTING.md

@@ -628,7 +628,7 @@ You'll need to modify the following files
 - `backend/s3/s3.go`
   - Add the provider to `providerOption` at the top of the file
   - Add endpoints and other config for your provider gated on the provider in `fs.RegInfo`.
-  - Exclude your provider from generic config questions (eg `region` and `endpoint).
+  - Exclude your provider from generic config questions (eg `region` and `endpoint`).
   - Add the provider to the `setQuirks` function - see the documentation there.
 - `docs/content/s3.md`
   - Add the provider at the top of the page.