test: enable IE10 by skipping dataset tests

Closes #472.

browserstack-karma.js

@@ -91,7 +91,6 @@ module.exports = {
     os: 'Windows',
     os_version: '7',
   },
-  /* https://github.com/snabbdom/snabbdom/issues/472
   BS_IE_10: {
     base: 'BrowserStack',
     browser: 'ie',
@@ -99,5 +98,4 @@ module.exports = {
     os: 'Windows',
     os_version: '7',
   },
-  */
 };

src/test/dataset.ts

@@ -9,6 +9,12 @@ var patch = init([
 ]);
 
 describe('dataset', function () {
+  before(function () {
+    if (!Object.hasOwnProperty.call(HTMLElement.prototype, 'dataset')) {
+      this.skip();
+    }
+  });
+
   var elm: any, vnode0: any;
   beforeEach(function () {
     elm = document.createElement('div');