changed var to const 2 (#13068)

* changed var to const

* fixed typo created in last commit

* added or empty object to options in prometheus/datasource

public/app/plugins/datasource/postgres/response_parser.ts

@@ -4,7 +4,7 @@ export default class ResponseParser {
   constructor(private $q) {}
 
   processQueryResult(res) {
-    var data = [];
+    const data = [];
 
     if (!res.data.results) {
       return { data: data };