Upgrade core to ddc431 (#715)

Author: macpie

rebar.lock

@@ -9,7 +9,7 @@
   0},
  {<<"blockchain">>,
   {git,"https://github.com/helium/blockchain-core.git",
-       {ref,"dae09a8000ac2c45f34dc57a8a1a9de9b083b0b0"}},
+       {ref,"ddc431a1a3de4e7b9708f4559f00625c0e5f979b"}},
   0},
  {<<"certifi">>,{pkg,<<"certifi">>,<<"2.9.0">>},1},
  {<<"chatterbox">>,