gulp docs fails on node v12.18.4 - (Chart.js 2.9)

[alessandroasm]

Expected Behavior

gulp docs succeeds

Current Behavior

[14:25:36] Using gulpfile ~/src/github/Chart.js/gulpfile.js
[14:25:36] Starting 'docs'...
info: installing 5 plugins using npm@3.9.2 
info:  
info: installing plugin "search-plus" 
info: install plugin "search-plus" (*) from NPM with version 1.0.3 
/home/alessandro/src/github/Chart.js/node_modules/npm/node_modules/graceful-fs/polyfills.js:287
      if (cb) cb.apply(this, arguments)
                 ^

TypeError: cb.apply is not a function
    at /home/alessandro/src/github/Chart.js/node_modules/npm/node_modules/graceful-fs/polyfills.js:287:18
    at FSReqCallback.oncomplete (fs.js:169:5)

Possible Solution

Steps to Reproduce

Run gulp docs on node v12.18.4

Context

This is blocking PRs on 2.9 branch:
PR #7853
PR #7854

Related issue: GitbookIO/gitbook-cli#110

Environment

• Chart.js version: 2.9
• Browser name and version:
• Link to your project:

[alessandroasm]

The issue is that gitbook-cli still uses old dependencies that are not compatible with node v12.18.3 or later, specifically graceful-fs v4.1.11.

This happens because an optional options argument was added to fs.fstat:
https://nodejs.org/dist/latest-v12.x/docs/api/fs.html#fs_fs_fstat_fd_options_callback

Since gitbook-cli is deprecated, I'm thinking about pushing a PR forcing travis to use node v12.18.2.