fix(core): only import typing from zone.js

[JiaLiPassion]

Checklist

• Issue number for this PR: Error: Zone already loaded. #1597 (required)
• Docs included?: no (yes/no; required for all API/functional changes)
• Test units included?: no (yes/no; required)
• In a clean directory, yarn install, yarn test run successfully? yes (yes/no; required)

Description

Should only import {} from 'zone.js' to import typing, but not import zone.js again, otherwise it will report Zone is already loaded error.

Code sample

@jamesdaniels , please review, thank you.

[pookdeveloper]

If I genereta ionic start coference, i get the same error when install de plugin

[paulstelzer]

Changing the import did not work for me. I had to remove the complete line to make my application work again (using Ionic)

[pookdeveloper]

Not work if use firebase and ionic conference example

[JiaLiPassion]

@pookdeveloper , could you provide a reproduce repo?

[pookdeveloper]

@JiaLiPassion Hellou I only generate the ionic start with template conference, and then install firebase and make the change to

import {} from 'zone.js';

try those steps and comment, thanks

[JiaLiPassion]

@pookdeveloper , after install angularfire2 from npm, even you change the src to

import {} from 'zone.js';

It will not be loaded into bundle, could you try this zip https://github.com/angular/angularfire2/files/1977627/dist.zip to replace node_modules/angularfire2/

[jamesdaniels]

Thanks for the fix

[LRonHubs]

This zip did not work for me or fix it