fix instances of filebeat instead of metricbeat

x-pack/metricbeat/mbreceiver/config.go

@@ -6,8 +6,8 @@ package mbreceiver
 
 import "fmt"
 
-// Config is config settings for filebeat receiver.  The structure of
-// which is the same as the filebeat.yml configuration file.
+// Config is config settings for metricbeat receiver.  The structure of
+// which is the same as the metricbeat.yml configuration file.
 type Config struct {
 	Beatconfig map[string]interface{} `mapstructure:",remain"`
 }