Update hacking-on-gitea.en-us.md (#8275)

Fix spelling of misspell in command to validate swagger.

docs/content/doc/advanced/hacking-on-gitea.en-us.md

@@ -178,7 +178,7 @@ make generate-swagger
 You should validate your generated Swagger file and spell-check it with:
 
 ```bash
-make swagger-validate mispell-check
+make swagger-validate misspell-check
 ```
 
 You should commit the changed swagger JSON file. The continous integration