build: pin gpb 4.11.2

gpb is only to compile protobuf,
it is not included in release tarball.
for some reason rebar3 fetches an unknown version without this pin

rebar.config

@@ -36,7 +36,8 @@
 {erl_first_files, ["src/emqx_logger.erl", "src/emqx_rule_actions_trans.erl"]}.
 
 {deps,
-    [ {ehttpc, {git, "https://github.com/emqx/ehttpc", {tag, "0.1.5"}}}
+    [ {gpb, "4.11.2"} %% gpb only used to build, but not for release, pin it here to avoid fetching a wrong version due to rebar plugins scattered in all the deps
+    , {ehttpc, {git, "https://github.com/emqx/ehttpc", {tag, "0.1.5"}}}
     , {eredis_cluster, {git, "https://github.com/emqx/eredis_cluster", {tag, "0.6.5"}}}
     , {gproc, {git, "https://github.com/uwiger/gproc", {tag, "0.8.0"}}}
     , {jiffy, {git, "https://github.com/emqx/jiffy", {tag, "1.0.5"}}}