node 10 isn't compatible

In doc/prepare.md is written:

Node 6.x or newer

but using node 10 I have this error when doing gdk update:

cd /home/rpadovani/gitlab/gitlab-development-kit/gitlab && yarn install --pure-lockfile
yarn install v1.6.0
(node:17980) [DEP0005] DeprecationWarning: Buffer() is deprecated due to security and usability issues. Please use the Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() methods instead.
[1/4] Resolving packages...
[2/4] Fetching packages...
error upath@1.0.2: The engine "node" is incompatible with this module. Expected version ">=4 <=9".
error Found incompatible module
info Visit https://yarnpkg.com/en/docs/cli/install for documentation about this command.
Makefile:73: recipe for target '.gitlab-yarn' failed
make: *** [.gitlab-yarn] Error 1

using node9 everything is fine.

I suggest to highlight it somehow (or update the yarn lockfile in Gitlab: https://github.com/anodynos/upath/issues/14)