changed "flush_interval" into "$flush_interval"

Author: janvda

telegraf/telegraf.conf

@@ -50,7 +50,7 @@
 
   ## Default flushing interval for all outputs. You shouldn't set this below
   ## interval. Maximum flush_interval will be flush_interval + flush_jitter
-  flush_interval = "flush_interval"
+  flush_interval = "$flush_interval"
 
   ## Jitter the flush interval by a random amount. This is primarily to avoid
   ## large write spikes for users running a large number of telegraf instances.