Update dependencies, pin grpc<1.27

[yurishkuro]

• Pin grpc to <1.27 (as a companion to Revert latest gRPC changes to allow more flexibility in versions #2018), to protect against breaking changes (balancer/resolver: remove temporary backward-compatibility type aliases grpc/grpc-go#3309) to the balancer pkg which is considered "experimental"
• Run dep ensure --update

NB: I am checking when our internal monorepo is going to upgrade grpc version so that we can remove the pin.

[codecov]

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