Use blocked scoped variables

In addition to using const and let, this also upgrades our linter config and removes lint (mostly whitespace).

examples/attributions.js

@@ -5,10 +5,10 @@ import Attribution from '../src/ol/control/Attribution.js';
 import TileLayer from '../src/ol/layer/Tile.js';
 import OSM from '../src/ol/source/OSM.js';
 
-var attribution = new Attribution({
+const attribution = new Attribution({
   collapsible: false
 });
-var map = new Map({
+const map = new Map({
   layers: [
     new TileLayer({
       source: new OSM()
@@ -23,7 +23,7 @@ var map = new Map({
 });
 
 function checkSize() {
-  var small = map.getSize()[0] < 600;
+  const small = map.getSize()[0] < 600;
   attribution.setCollapsible(small);
   attribution.setCollapsed(small);
 }