Fix/on deploy to netlify

[alexmndzdev]

This change is in order to fix this issue: https://github.com/decaporg/gatsby-starter-decap-cms/issues/912

What kind of change does this PR introduce? Bugfix, changing node version

Does this PR introduce a breaking change? It seems like not

What needs to be documented once your changes are merged? The minimun node version in README is already changed

[alexmndzdev]

It seems like throws an error at the deploy in netlify, the same thing passed to me, but you only need to clean cache and retry deploy again, that works for me. You can go to /admin in my fork: https://fix-gatsby-starter-decap-cms.netlify.app/

[hktari]

please merge this into main branch