Fix with-firebase-cloud-messaging example setup code

[aviaryan]

This PR updates the FCM setup code which should fix the issue #10628. This change is needed after firebase v7.0.0 because of a breaking change.

Official docs don't reflect this as of this moment. More details here. firebase/quickstart-js#422

[ijjk]

Stats from current PR

Default Server Mode

General

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
buildDuration	9.4s	9.7s	⚠️ +366ms
nodeModulesSize	56.2 MB	56.2 MB	✓

Client Bundles (main, webpack, commons)

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
main-HASH.js gzip	5.05 kB	5.05 kB	✓
webpack-HASH.js gzip	746 B	746 B	✓
de003c3a9d30..b61f.js gzip	12.3 kB	12.3 kB	✓
framework.HASH.js gzip	39.1 kB	39.1 kB	✓
Overall change	57.2 kB	57.2 kB	✓

Client Bundles (main, webpack, commons) Modern

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
main-HASH.module.js gzip	4.14 kB	4.14 kB	✓
webpack-HASH..dule.js gzip	746 B	746 B	✓
de003c3a9d30..dule.js gzip	9.22 kB	9.22 kB	✓
framework.HA..dule.js gzip	39.1 kB	39.1 kB	✓
Overall change	53.2 kB	53.2 kB	✓

Legacy Client Bundles (polyfills)

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
polyfills-HASH.js gzip	18.9 kB	18.9 kB	✓
Overall change	18.9 kB	18.9 kB	✓

Client Pages

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
_app.js gzip	1.06 kB	1.06 kB	✓
_error.js gzip	2.98 kB	2.98 kB	✓
hooks.js gzip	664 B	664 B	✓
index.js gzip	222 B	222 B	✓
link.js gzip	1.9 kB	1.9 kB	✓
routerDirect.js gzip	279 B	279 B	✓
withRouter.js gzip	278 B	278 B	✓
Overall change	7.38 kB	7.38 kB	✓

Client Pages Modern

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
_app.module.js gzip	577 B	577 B	✓
_error.module.js gzip	2.08 kB	2.08 kB	✓
hooks.module.js gzip	370 B	370 B	✓
index.module.js gzip	212 B	212 B	✓
link.module.js gzip	1.48 kB	1.48 kB	✓
routerDirect..dule.js gzip	271 B	271 B	✓
withRouter.m..dule.js gzip	270 B	270 B	✓
Overall change	5.26 kB	5.26 kB	✓

Client Build Manifests

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
_buildManifest.js gzip	61 B	61 B	✓
_buildManife..dule.js gzip	61 B	61 B	✓
Overall change	122 B	122 B	✓

Rendered Page Sizes

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
index.html gzip	924 B	924 B	✓
link.html gzip	934 B	934 B	✓
withRouter.html gzip	922 B	922 B	✓
Overall change	2.78 kB	2.78 kB	✓

---

Serverless Mode (Decrease detected ✓)

General

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
buildDuration	10s	11.2s	⚠️ +1.3s
nodeModulesSize	56.2 MB	56.2 MB	✓

Client Bundles (main, webpack, commons)

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
main-HASH.js gzip	5.05 kB	5.05 kB	✓
webpack-HASH.js gzip	746 B	746 B	✓
de003c3a9d30..b61f.js gzip	12.3 kB	12.3 kB	✓
framework.HASH.js gzip	39.1 kB	39.1 kB	✓
Overall change	57.2 kB	57.2 kB	✓

Client Bundles (main, webpack, commons) Modern

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
main-HASH.module.js gzip	4.14 kB	4.14 kB	✓
webpack-HASH..dule.js gzip	746 B	746 B	✓
de003c3a9d30..dule.js gzip	9.22 kB	9.22 kB	✓
framework.HA..dule.js gzip	39.1 kB	39.1 kB	✓
Overall change	53.2 kB	53.2 kB	✓

Legacy Client Bundles (polyfills)

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
polyfills-HASH.js gzip	18.9 kB	18.9 kB	✓
Overall change	18.9 kB	18.9 kB	✓

Client Pages

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
_app.js gzip	1.06 kB	1.06 kB	✓
_error.js gzip	2.98 kB	2.98 kB	✓
hooks.js gzip	664 B	664 B	✓
index.js gzip	222 B	222 B	✓
link.js gzip	1.9 kB	1.9 kB	✓
routerDirect.js gzip	279 B	279 B	✓
withRouter.js gzip	278 B	278 B	✓
Overall change	7.38 kB	7.38 kB	✓

Client Pages Modern

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
_app.module.js gzip	577 B	577 B	✓
_error.module.js gzip	2.08 kB	2.08 kB	✓
hooks.module.js gzip	370 B	370 B	✓
index.module.js gzip	212 B	212 B	✓
link.module.js gzip	1.48 kB	1.48 kB	✓
routerDirect..dule.js gzip	271 B	271 B	✓
withRouter.m..dule.js gzip	270 B	270 B	✓
Overall change	5.26 kB	5.26 kB	✓

Client Build Manifests

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
_buildManifest.js gzip	61 B	61 B	✓
_buildManife..dule.js gzip	61 B	61 B	✓
Overall change	122 B	122 B	✓

Serverless bundles Overall decrease ✓

	zeit/next.js canary	aviaryan/next.js fix-fcm-example	Change
_error.js gzip	290 kB	289 kB	-415 B
404.html gzip	1.33 kB	1.33 kB	✓
hooks.html gzip	963 B	963 B	✓
index.js gzip	289 kB	290 kB	⚠️ +572 B
link.js gzip	298 kB	298 kB	-46 B
routerDirect.js gzip	298 kB	296 kB	-1.59 kB
withRouter.js gzip	296 kB	298 kB	⚠️ +1.29 kB
Overall change	1.47 MB	1.47 MB	-186 B

Commit: 4985e3f

[aviaryan]

Update on this - firebase/quickstart-js#422 has been merged by the Firebase team which confirms this is the correct approach.

What do I need to do to get this PR ready for merge?

[timneutkens]

Thanks!