anchor.diff:  
     crypto = buildFromGitHub {
       version = 6;
  -    rev = "b8fe1690c61389d7d2a8074a507d1d40c5d30448";
  -    date = "2019-01-31";
  +    rev = "a4c6cb3142f211c99e4bf4cd769535b29a9b616f";
  +    date = "2019-02-19";
       owner = "golang";
       repo = "crypto";
  -    sha256 = "5e41ac7afa805e24394434a0aa647b08d3d525cc8c2413ba7a9dde20c3d1009a";
  +    sha256 = "617f52d219350adc3c3602ccecfb81abfaef02b64d7f1bce0232a8035c773619";
       goPackagePath = "golang.org/x/crypto";
       buildInputs = [
         net_crypto_lib
  
positive.code: 
    httpcache = buildFromGitHub {
      version = 6;
      rev = "c63ab54fda8f77302f8d414e19933f2b6026a089";
      owner  = "gregjones";
      repo   = "httpcache";
      sha256 = "iT6P6SwFkZifKeK1quUlDdocg2RDwxAb1iW9M8qAZyU=";
      date = "2018-11-10";
      propagatedBuildInputs = [
        diskv
        goleveldb
  
negative.code: 
    go-ipfs-files = buildFromGitHub {
      version = 6;
      rev = "b9ab5987284914bf7c73b9c450b2ae6777051a3d";
      owner  = "ipfs";
      repo   = "go-ipfs-files";
      sha256 = "c15656069849d27003c23faf64ced88bd8e34531993f7d0cb369a2a4acea334d";
      date = "2019-02-11";
      propagatedBuildInputs = [
        sys
      ];
  