[docs] Fix Grammar in Step 8. (vercel#42018)

Author: alphaxek

contributing/core/developing.md

@@ -30,7 +30,7 @@ To develop locally:
 1. In a new terminal, run `pnpm types` to compile declaration files from
    TypeScript.
    _Note: You may need to repeat this step if your types get outdated._
-1. When you changes are finished commit them to the branch:
+1. When your changes are finished, commit them to the branch:
    ```
    git add .
    git commit -m "DESCRIBE_YOUR_CHANGES_HERE"