fix(package): update pnp-webpack-plugin to version 1.3.1

Closes #66

Author: greenkeeper[bot]

package.json

@@ -36,7 +36,7 @@
     "lint-staged": "8.1.0",
     "mini-css-extract-plugin": "0.4.5",
     "optimize-css-assets-webpack-plugin": "5.0.1",
-    "pnp-webpack-plugin": "1.2.1",
+    "pnp-webpack-plugin": "1.3.1",
     "postcss-flexbugs-fixes": "4.1.0",
     "postcss-loader": "3.0.0",
     "postcss-preset-env": "6.4.0",