fix all go style mistakes about fmt.Errorf

controllers/nginx/pkg/cmd/controller/nginx.go

@@ -441,7 +441,7 @@ func (n NGINXController) Check(_ *http.Request) error {
 	}
 	defer res.Body.Close()
 	if res.StatusCode != 200 {
-		return fmt.Errorf("Ingress controller is not healthy")
+		return fmt.Errorf("ingress controller is not healthy")
 	}
 	return nil
 }

controllers/nginx/pkg/metric/collector/status.go

@@ -138,7 +138,7 @@ func (bit BoolToFloat64) UnmarshalJSON(data []byte) error {
 	} else if asString == "0" || asString == "false" {
 		bit = 0
 	} else {
-		return fmt.Errorf(fmt.Sprintf("Boolean unmarshal error: invalid input %s", asString))
+		return fmt.Errorf(fmt.Sprintf("boolean unmarshal error: invalid input %s", asString))
 	}
 	return nil
 }