Bump minimal nodejs version in README.md (#183)
Bump minimal nodejs version in README.md (#183)

Since the 10.0.0 release, the minimal nodejs version as been bump to 12 according to this [comment](https://github.com/ai/autoprefixer-rails/issues/178#issuecomment-693096133)
ai/autoprefixer-rails,ai/autoprefixer-rails,ai/autoprefixer-rails,ai/autoprefixer-rails