Add check if crypto.getRandomValues is available

[neelance]

On some IE11 the randomBytes helper crashes with "TypeError: getRandomValues is not defined". The reason is not clear, maybe something pollutes self.crypto with a bad polyfill. Nevertheless it makes sense to fall back to Math.random if crypto.getRandomValues is not available.

[changeset-bot]

🦋 Changeset is good to go

Latest commit: 81d4de5

We got this.

This PR includes changesets to release 9 packages

Name	Type
@firebase/firestore	Patch
firebase	Patch
firebase-firestore-integration-test	Patch
@firebase/testing	Patch
firebase-browserify-test	Patch
firebase-package-typings-test	Patch
firebase-messaging-selenium-test	Patch
firebase-typescript-test	Patch
firebase-webpack-test	Patch

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[neelance]

@googlebot I signed it!

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[neelance]

@schmidt-sebastian Mind taking a look? :)