src: include uv.h in node_binding header

This was removed in https://github.com/nodejs/node/commit/3bb085dbad4d23030c731834e35b2804c8a50b23 but is needed by Electron on Windows, as otherwise compilation errors will occur as a result of unknown libuv types:

In file included from ../../third_party/electron_node/src/node_binding.cc:1:
../../third_party/electron_node/src/node_binding.h(76,3): error: unknown type name 'uv_lib_t'
  uv_lib_t lib_;
  ^

See https://ci.appveyor.com/project/electron-bot/electron-ljo26/builds/29979721.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines