fix(deps): update dependency rollup-plugin-postcss to v3.1.8 (#312)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

Author: renovate[bot]

package-lock.json

@@ -88,7 +88,7 @@
     "rollup-plugin-analyzer": "3.3.0",
     "rollup-plugin-babel": "4.4.0",
     "rollup-plugin-copy": "3.3.0",
-    "rollup-plugin-postcss": "3.1.6",
+    "rollup-plugin-postcss": "3.1.8",
     "rollup-plugin-terser": "7.0.1",
     "rollup-plugin-typescript2": "0.27.2",
     "yargs": "15.4.1"