fix(electron): postcss config

Author: timsuchanek

packages/graphql-playground-electron/postcss.config.js

@@ -4,7 +4,7 @@ module.exports = ctx => ({
       variables: () => require('graphcool-styles/dist/variables/variables.js'),
     }),
     require('postcss-inherit')({
-      globalStyles: 'node_modules/graphcool-styles/dist/styles.css',
+      globalStyles: '../../node_modules/graphcool-styles/dist/styles.css',
       propertyRegExp: /^(inherit|extend|p)s?:?$/i,
     }),
   ],