fix(restart): typescript fix for browser.restart

closes #3648

Author: cnishina

lib/runner.ts

@@ -258,7 +258,8 @@ export class Runner extends EventEmitter {
       // calls here are not guaranteed to complete before the tests resume.
       this.driverprovider_.quitDriver(browser_.driver);
       // Copy mock modules, but do not navigate to previous URL.
-      browser_ = browser_.forkNewDriverInstance(false, true);
+      let forkBrowser = browser_.forkNewDriverInstance(false, true);
+      browser_.driver = forkBrowser.driver;
       this.setupGlobals_(browser_);
     };