chore: update grpc vsn in mix.exs

mix.exs

@@ -54,7 +54,7 @@ defmodule EMQXUmbrella.MixProject do
       {:esockd, github: "emqx/esockd", tag: "5.9.4", override: true},
       {:ekka, github: "emqx/ekka", tag: "0.13.4", override: true},
       {:gen_rpc, github: "emqx/gen_rpc", tag: "2.8.1", override: true},
-      {:grpc, github: "emqx/grpc-erl", tag: "0.6.6", override: true},
+      {:grpc, github: "emqx/grpc-erl", tag: "0.6.7", override: true},
       {:minirest, github: "emqx/minirest", tag: "1.3.7", override: true},
       {:ecpool, github: "emqx/ecpool", tag: "0.5.2"},
       {:replayq, "0.3.4", override: true},