core dump on TravisCI

[unional]

$ npm install -g greenkeeper-lockfile@1
npm WARN npm npm does not support Node.js v9.0.0
npm WARN npm You should probably upgrade to a newer version of node as we
npm WARN npm can't make any promises that npm will work with this version.
npm WARN npm Supported releases of Node.js are the latest release of 4, 6, 7, 8.
npm WARN npm You can find the latest version at https://nodejs.org/
/home/travis/.nvm/versions/node/v9.0.0/bin/node[2988]: ../src/node_zlib.cc:430:static void node::{anonymous}::ZCtx::Init(const v8::FunctionCallbackInfo<v8::Value>&): Assertion `args.Length() == 7 && "init(windowBits, level, memLevel, strategy, writeResult, writeCallback," " dictionary)"' failed.
 1: node::Abort() [npm]
 2: node::Assert(char const* const (*) [4]) [npm]
 3: 0x1251ea1 [npm]
 4: v8::internal::FunctionCallbackArguments::Call(void (*)(v8::FunctionCallbackInfo<v8::Value> const&)) [npm]
 5: 0xb74c3c [npm]
 6: v8::internal::Builtin_HandleApiCall(int, v8::internal::Object**, v8::internal::Isolate*) [npm]
 7: 0x111383e042fd
/home/travis/.travis/job_stages: line 57:  2988 Aborted                 (core dumped) npm install -g greenkeeper-lockfile@1
The command "npm install -g greenkeeper-lockfile@1" failed and exited with 134 during .
Your build has been stopped.

Likely it's npm@5 + node@9.0.0 issue. Checking on it....

[Realtin]

Thank you for raising this issue! ✨