test: fix webworker tests

Author: daviddias

test/browser.js

@@ -1,15 +1,16 @@
 /* eslint-env mocha */
+/* global self */
 'use strict'
 
 const series = require('async/series')
 const IPFSRepo = require('ipfs-repo')
 
 const tests = require('./block-service-test')
 
-const idb = window.indexedDB ||
-        window.mozIndexedDB ||
-        window.webkitIndexedDB ||
-        window.msIndexedDB
+const idb = self.indexedDB ||
+        self.mozIndexedDB ||
+        self.webkitIndexedDB ||
+        self.msIndexedDB
 
 idb.deleteDatabase('ipfs')
 idb.deleteDatabase('ipfs/blocks')