chore(package): update jsdom to version 15.2.1

Closes #35

Author: greenkeeper[bot]

package.json

@@ -37,7 +37,7 @@
     "babel-register": "^6.24.1",
     "eslint": "^4.1.0",
     "istanbul": "^0.4.5",
-    "jsdom": "^11.0.0",
+    "jsdom": "^15.2.1",
     "mocha": "^5.0.0",
     "nyc": "^12.0.2",
     "preact": "^8.1.0",