Rename "scrape_failures" to "scrape_failures_total"

This metric expresses a sum / accumulating unit, and should thusly be
suffixed with total[1]

https://prometheus.io/docs/practices/naming/#metric-names

collector.go

@@ -57,7 +57,7 @@ func (e *Exporter) newCollector() *collector {
 		maxActiveProcesses: newFuncMetric("active_max_processes", "Maximum active process count"),
 		maxChildrenReached: newFuncMetric("max_children_reached_total", "Number of times the process limit has been reached"),
 		slowRequests:       newFuncMetric("slow_requests_total", "Number of requests that exceed request_slowlog_timeout"),
-		scrapeFailures:     newFuncMetric("scrape_failures", "Number of errors while scraping php_fpm"),
+		scrapeFailures:     newFuncMetric("scrape_failures_total", "Number of errors while scraping php_fpm"),
 	}
 }