Bump google.golang.org/grpc from 1.37.0 to 1.56.3 (#90)

Bumps [google.golang.org/grpc](https://github.com/grpc/grpc-go) from 1.37.0 to 1.56.3.
- [Release notes](https://github.com/grpc/grpc-go/releases)
- [Commits](grpc/grpc-go@v1.37.0...v1.56.3)

---
updated-dependencies:
- dependency-name: google.golang.org/grpc
  dependency-type: direct:production
...

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go.mod

@@ -4,6 +4,6 @@ go 1.15
 
 require (
 	github.com/openconfig/ygot v0.13.2
-	google.golang.org/grpc v1.37.0
-	google.golang.org/protobuf v1.26.0
+	google.golang.org/grpc v1.56.3
+	google.golang.org/protobuf v1.30.0
 )