Use blocked scoped variables

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

examples/modify-features.js

@@ -10,11 +10,11 @@ import OSM from '../src/ol/source/OSM.js';
 import VectorSource from '../src/ol/source/Vector.js';
 
 
-var raster = new TileLayer({
+const raster = new TileLayer({
   source: new OSM()
 });
 
-var vector = new VectorLayer({
+const vector = new VectorLayer({
   source: new VectorSource({
     url: 'data/geojson/countries.geojson',
     format: new GeoJSON(),
@@ -22,15 +22,15 @@ var vector = new VectorLayer({
   })
 });
 
-var select = new Select({
+const select = new Select({
   wrapX: false
 });
 
-var modify = new Modify({
+const modify = new Modify({
   features: select.getFeatures()
 });
 
-var map = new Map({
+const map = new Map({
   interactions: defaultInteractions().extend([select, modify]),
   layers: [raster, vector],
   target: 'map',