Update rollup-plugin-postcss to the latest version 🚀 (#83)

Author: greenkeeper[bot]

package-lock.json

@@ -95,7 +95,7 @@
     "rollup-plugin-filesize": "^7.0.0",
     "rollup-plugin-local-resolve": "^1.0.7",
     "rollup-plugin-peer-deps-external": "^2.2.2",
-    "rollup-plugin-postcss": "^2.1.1",
+    "rollup-plugin-postcss": "^3.0.0",
     "sass": "^1.26.1",
     "sass-loader": "^8.0.2",
     "semantic-release": "^17.0.4",