chore(rebar.config): use hocon 0.6.0

hocon 0.6.0 added supports for sensitive config flagging
sub-struct type checking, and remote struct referencing

apps/emqx/rebar.config

@@ -16,7 +16,7 @@
     , {ekka, {git, "https://github.com/emqx/ekka", {tag, "0.10.1"}}}
     , {gen_rpc, {git, "https://github.com/emqx/gen_rpc", {tag, "2.5.1"}}}
     , {cuttlefish, {git, "https://github.com/emqx/cuttlefish", {tag, "v4.0.1"}}} %% todo delete when plugins use hocon
-    , {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.5.1"}}}
+    , {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.6.0"}}}
     , {pbkdf2, {git, "https://github.com/emqx/erlang-pbkdf2.git", {branch, "2.0.4"}}}
     , {recon, {git, "https://github.com/ferd/recon", {tag, "2.5.1"}}}
     , {snabbkaffe, {git, "https://github.com/kafka4beam/snabbkaffe.git", {tag, "0.13.0"}}}

rebar.config

@@ -52,7 +52,7 @@
     , {observer_cli, "1.6.1"} % NOTE: depends on recon 2.5.1
     , {getopt, "1.0.1"}
     , {snabbkaffe, {git, "https://github.com/kafka4beam/snabbkaffe.git", {tag, "0.13.0"}}}
-    , {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.5.1"}}}
+    , {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.6.0"}}}
     , {emqx_http_lib, {git, "https://github.com/emqx/emqx_http_lib.git", {tag, "0.2.1"}}}
     ]}.