See if there is any way to remove the custom sass loader in "plugins"

[sraby]

We have a "plugins" subdirectory that seems to include a blank package.json file and another file that seems to be copy/pasted from the gatsby-plugin-postcss-sass source code. Is there a more graceful way to implement this functionality?

[sraby]

After further review of the gatsby-plugin-sass plugin that we need to fix this, it seems we actually need to upgrade to gatsby v2 first. So, we should address this issue after addressing #88.