Update the LastMapUpdate timestamp in all cases.

It used to be that in case of errors we didn't update
the "last" timestamp, meaning that we could potentially call
the costly UpdateMap function too often. Closes elastic#7.

procs/procs.go

@@ -226,7 +226,10 @@ func (proc *ProcessesWatcher) FindProc(port uint16) (procname string) {
 		return p.Proc.Name
 	}
 
-	if time.Now().Sub(proc.LastMapUpdate) > proc.MaxReadFreq {
+	now := time.Now()
+
+	if now.Sub(proc.LastMapUpdate) > proc.MaxReadFreq {
+		proc.LastMapUpdate = now
 		proc.UpdateMap()
 
 		// try again
@@ -294,7 +297,6 @@ func (proc *ProcessesWatcher) UpdateMap() {
 		}
 	}
 
-	proc.LastMapUpdate = time.Now()
 }
 
 // Parses the /proc/net/tcp file