Update rebar.config (#2877)

rebar.config

@@ -2,8 +2,8 @@
     [{jsx, "2.9.0"}, % hex
      {cowboy, "2.6.1"}, % hex
      {gproc, "0.8.0"}, % hex
-     {esockd, "5.5.0"}, %hex
-     {ekka, "0.6.1"}, %hex
+     {esockd, {git, "https://github.com/emqx/esockd", {tag, "v5.5.1"}}},
+     {ekka, {git, "https://github.com/emqx/ekka", {tag, "v0.6.2"}}},
      {gen_rpc, {git, "https://github.com/emqx/gen_rpc", {tag, "2.4.1"}}},
      {cuttlefish, {git, "https://github.com/emqx/cuttlefish", {tag, "v3.0.0"}}}
     ]}.