add back support for standard prettier config options

[deecewan]

Feels like the whole point of prettier is that 1 .prettierrc sets the config for the whole project. So, to me, it's a little weird that the ruby plugin has different options to the standard package

Couldn't find any tests for single quotes or trailing commas in the codebase, and not 100% sure where they should go, so happy to add some if you point me to where.

Closes #1239