chore: update rebar.conf in emqx_exproto

apps/emqx_exproto/rebar.config

@@ -1,4 +1,5 @@
 {erl_opts, [debug_info]}.
+{deps, []}.
 
 {plugins, [
     {grpc_plugin, {git, "https://github.com/HJianBo/grpc_plugin", {tag, "v0.10.2"}}}