upgrade relx lock to include heart fix

rebar.config

@@ -9,7 +9,7 @@
         {getopt,              "1.0.1"},
         {bbmustache,          "1.8.0"},
         %% {relx,                "3.33.0"},
-        {relx, {git, "https://github.com/erlware/relx.git", {tag, "v4.0.0-rc1"}}},
+        {relx, {git, "https://github.com/erlware/relx.git", {branch, "4.0.0"}}},
         {cf,                  "0.2.2"},
         {cth_readable,        "1.4.8"},
         {eunit_formatters,    "0.5.0"}]}.

rebar.lock

@@ -10,7 +10,7 @@
  {<<"providers">>,{pkg,<<"providers">>,<<"1.8.1">>},0},
  {<<"relx">>,
   {git,"https://github.com/erlware/relx.git",
-       {ref,"e3b61cd8eab04609c4b0e684dfb564e788446d53"}},
+       {ref,"ac5bb88330e23b29ae0449214af5f62bd16ecdce"}},
   0},
  {<<"ssl_verify_fun">>,{pkg,<<"ssl_verify_fun">>,<<"1.1.5">>},0}]}.
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