fix(deps): Update dependency @grpc/grpc-js to v1.12.2 (#81)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [@grpc/grpc-js](https://grpc.io/) ([source](https://togithub.com/grpc/grpc-node)) | devDependencies | minor | [`1.11.3` -> `1.12.2`](https://renovatebot.com/diffs/npm/@grpc%2fgrpc-js/1.11.3/1.12.2) |

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### Release Notes

<details>
<summary>grpc/grpc-node (@&#8203;grpc/grpc-js)</summary>

### [`v1.12.2`](https://togithub.com/grpc/grpc-node/releases/tag/%40grpc/grpc-js%401.12.2): @&#8203;grpc/grpc-js 1.12.2

[Compare Source](https://togithub.com/grpc/grpc-node/compare/@grpc/[email protected]...@grpc/[email protected])

-   Use `util.promisify` instead of `fs/promises` for Node 12 compatibility ([#&#8203;2838](https://togithub.com/grpc/grpc-node/issues/2838))

### [`v1.12.1`](https://togithub.com/grpc/grpc-node/releases/tag/%40grpc/grpc-js%401.12.1): @&#8203;grpc/grpc-js 1.12.1

[Compare Source](https://togithub.com/grpc/grpc-node/compare/@grpc/[email protected]...@grpc/[email protected])

-   Port bugfixes from 1.11.x into 1.12.x ([#&#8203;2836](https://togithub.com/grpc/grpc-node/issues/2836))

### [`v1.12.0`](https://togithub.com/grpc/grpc-node/releases/tag/%40grpc/grpc-js%401.12.0): @&#8203;grpc/grpc-js 1.12.0

[Compare Source](https://togithub.com/grpc/grpc-node/compare/@grpc/[email protected]...@grpc/[email protected])

#### Changelog

-   Provide the method_name for the CallCredentials callback generateMetadata ([#&#8203;2814](https://togithub.com/grpc/grpc-node/issues/2814) contributed by [@&#8203;becoded](https://togithub.com/becoded))
-   Add an optional `rejectUnauthorized` field to the `VerifyOptions` interface, which can be passed as an argument to `credentials.createSsl` and `createFromSecureContext` ([#&#8203;2812](https://togithub.com/grpc/grpc-node/issues/2812) contributed by [@&#8203;vinothsa4891](https://togithub.com/vinothsa4891))

#### Experimental API changes

Added:

-   `CaCertificateUpdate`
-   `CaCertificateUpdateListener`
-   `IdentityCertificateUpdate`
-   `IdentityCertificateUpdateListener`
-   `CertificateProvider`
-   `FileWatcherCertificateProvider`
-   `FileWatcherCertificateProviderConfig`
-   `createCertificateProviderChannelCredentials`
-   `createCertificateProviderServerCredentials`

Modified:

-   `LoadBalancer`: The constructor now takes an additional argument of type `ChannelCredentials`.
-   `ChannelControlHelper#createSubchannel`: Now takes an additional argument of type `ChannelCredentials | null`. This should be passed along if overriding this function.
-   `LeafLoadBalancer`: The constructor now takes an additional argument of type `ChannelCredentials`.

</details>

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