- querylog: fix get data

Close #1589

Squashed commit of the following:

commit 83d1d15f06a67746feb0e82fb71d5ea02f86ab69
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Fri Apr 17 14:11:00 2020 +0300

    - querylog: fix get data

querylog/qlog.go

@@ -238,7 +238,7 @@ func (l *queryLog) getData(params getDataParams) map[string]interface{} {
 	entries := append(memoryEntries, fileEntries...)
 	if len(entries) > getDataLimit {
 		// remove extra records
-		entries = entries[(len(entries) - getDataLimit):]
+		entries = entries[:getDataLimit]
 	}
 	if len(entries) == getDataLimit {
 		// change the "oldest" value here.