docs: fix typo in CONTRIBUTING.md (#722)

Author: stainless-bot

CONTRIBUTING.md

@@ -68,7 +68,7 @@ pnpm link -—global openai
 Most tests require you to [set up a mock server](https://github.com/stoplightio/prism) against the OpenAPI spec to run the tests.
 
 ```bash
-npx prism path/to/your/openapi.yml
+npx prism mock path/to/your/openapi.yml
 ```
 
 ```bash