Use blocked scoped variables

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

examples/wms-capabilities.js

@@ -1,10 +1,10 @@
 import WMSCapabilities from '../src/ol/format/WMSCapabilities.js';
 
-var parser = new WMSCapabilities();
+const parser = new WMSCapabilities();
 
 fetch('data/ogcsample.xml').then(function(response) {
   return response.text();
 }).then(function(text) {
-  var result = parser.read(text);
+  const result = parser.read(text);
   document.getElementById('log').innerText = JSON.stringify(result, null, 2);
 });