Update x-pack/elastic-agent/GUIDELINES.md

Co-authored-by: Gil Raphaelli <[email protected]>

x-pack/elastic-agent/GUIDELINES.md

@@ -4,6 +4,6 @@ This document contains architecture details around Elastic Agent and guidelines
 
 ## Processes running as service and error handling
 
-All the processes started by Elastic Agent are running as service. Each service is expected to handle local errors on its own and continue working. A process should only fail on startup if a non valid configuration is passed in. As soon as a process is running and partial updates to the config are made without restart, the service is expected to keep running but report the errors.
+All the processes started by Elastic Agent are running as service. Each service is expected to handle local errors on its own and continue working. A process should only fail on startup if an invalid configuration is passed in. As soon as a process is running and partial updates to the config are made without restart, the service is expected to keep running but report the errors.
 
 A service that needs to do setup tasks on startup is expected to retry until it succeeds and not error out after a certain timeout.