Consistently use lowercase HTML tag names

Unlike HTML, XHTML is case-sensitive.

test/spec/ol/control/control.test.js

@@ -8,7 +8,7 @@ describe('ol.control.Control', function() {
     map = new Map({
       target: document.createElement('div')
     });
-    const element = document.createElement('DIV');
+    const element = document.createElement('div');
     control = new Control({element: element});
     control.setMap(map);
   });

test/spec/ol/format/gml.test.js

@@ -14,7 +14,7 @@ import {createElementNS, parse} from '../../../../src/ol/xml.js';
 const readGeometry = function(format, text, opt_options) {
   const doc = parse(text);
   // we need an intermediate node for testing purposes
-  const node = document.createElement('PRE');
+  const node = document.createElement('pre');
   node.appendChild(doc.documentElement);
   return format.readGeometryFromNode(node, opt_options);
 };

test/spec/ol/mapbrowserevent.test.js

@@ -15,7 +15,7 @@ describe('ol.MapBrowserEventHandler', function() {
 
     beforeEach(function() {
       clock = sinon.useFakeTimers();
-      target = document.createElement('DIV');
+      target = document.createElement('div');
       handler = new MapBrowserEventHandler(new Map({
         target: target
       }));