upgrade relx version

vor 8 Jahren · 48565557e4
--- a/rebar.config
+++ b/rebar.config
@ -7,7 +7,7 @@
        {providers,           "1.6.0"},
        {getopt,              "0.8.2"},
        {bbmustache,          "1.0.4"},
        {relx,                "3.19.0"},
        {relx,                "3.20.0"},
        {cf,                  "0.2.1"},
        {cth_readable,        "1.2.3"},
        {eunit_formatters,    "0.3.1"}]}.