This allows removal of x/net/sync and x/net/context, which is a welcome
change.

BREAKING_CHANGE_ACCEPTABLE=protoc churn

Updates go.mod to include new version of gRPC, which removes its
dependency on the old github.com/golang/lint in favour of the new
golang.org/x/lint.

Relevant: https://github.com/google/go-genproto/pull/143

This commit was generated by go mod init && go mod tidy