Recommended environment for CONTRIBUTING.md

[takumi]

Describe the bug

Setup error when using node v13.x
If I tried node v12.x or below, setup is complete.
I wanted to describe the recommended environment for node and npm.

Environment:

• OS: Mac OSX
• Browser:
• Build environment (i.e. NodeJS): node v13.2.0

[B.C.Rikko]

Thanks for your report 🙇

I agree with writing a Node version on CONTRIBUTING.md. 👍
As I confirmed with node 10.x and 12.x version, I want to change the package.json as well.

ref #367