Change NIGHTFALL_GITHUB_TOKEN env var name (#3)

* Change var name

* Update error msg

Author: henkejosh

cmd/nightfalldlp/main.go

@@ -14,7 +14,7 @@ import (
 const (
 	nightfallConfigFileName = ".nightfalldlp/config.json"
 	githubActionsEnvVar     = "GITHUB_ACTIONS"
-	githubTokenEnvVar       = "NIGHTFALL_GITHUB_TOKEN"
+	githubTokenEnvVar       = "GITHUB_TOKEN"
 )
 
 // main starts the service process.
@@ -69,7 +69,7 @@ func CreateDiffReviewerClient() (diffreviewer.DiffReviewer, error) {
 	case usingGithubAction():
 		githubToken, ok := os.LookupEnv(githubTokenEnvVar)
 		if !ok {
-			return nil, errors.New("missing github token in env")
+			return nil, fmt.Errorf("could not find required %s environment variable", githubTokenEnvVar)
 		}
 		return github.NewAuthenticatedGithubService(githubToken), nil
 	default: