upgrade relx to 3.21.0

rebar.config

@@ -7,7 +7,7 @@
         {providers,           "1.6.0"},
         {getopt,              "0.8.2"},
         {bbmustache,          "1.0.4"},
-        {relx,                "3.20.0"},
+        {relx,                "3.21.0"},
         {cf,                  "0.2.1"},
         {cth_readable,        "1.2.3"},
         {eunit_formatters,    "0.3.1"}]}.

rebar.lock

@@ -7,7 +7,7 @@
  {<<"eunit_formatters">>,{pkg,<<"eunit_formatters">>,<<"0.3.1">>},0},
  {<<"getopt">>,{pkg,<<"getopt">>,<<"0.8.2">>},0},
  {<<"providers">>,{pkg,<<"providers">>,<<"1.6.0">>},0},
- {<<"relx">>,{pkg,<<"relx">>,<<"3.20.0">>},0},
+ {<<"relx">>,{pkg,<<"relx">>,<<"3.21.0">>},0},
  {<<"ssl_verify_fun">>,{pkg,<<"ssl_verify_fun">>,<<"1.1.1">>},0}]}.
 [
 {pkg_hash,[
@@ -19,6 +19,6 @@
  {<<"eunit_formatters">>, <<"7A6FC351EB5B873E2356B8852EB751E20C13A72FBCA03393CF682B8483509573">>},
  {<<"getopt">>, <<"B17556DB683000BA50370B16C0619DF1337E7AF7ECBF7D64FBF8D1D6BCE3109B">>},
  {<<"providers">>, <<"DB0E2F9043AE60C0155205FCD238D68516331D0E5146155E33D1E79DC452964A">>},
- {<<"relx">>, <<"B515B8317D25B3A1508699294C3D1FA6DC0527851DFFC87446661BCE21A36710">>},
+ {<<"relx">>, <<"91E1EA9F09B4EDFDA8461901F4B5C5E0226E43EC161E147EEAB29F7761DF6EB5">>},
  {<<"ssl_verify_fun">>, <<"28A4D65B7F59893BC2C7DE786DEC1E1555BD742D336043FE644AE956C3497FBE">>}]}
 ].