add postcss for proper css compiling

package.json

@@ -20,6 +20,7 @@
         "babel-register": "^6.26.0",
         "clean-webpack-plugin": "^0.1.19",
         "css-loader": "^0.28.11",
+        "cssnano": "^3.10.0",
         "extract-text-webpack-plugin": "^4.0.0-beta.0",
         "glob-all": "^3.1.0",
         "html-webpack-plugin": "^3.2.0",
@@ -31,6 +32,7 @@
         "postcss-import": "^11.1.0",
         "postcss-loader": "^2.1.5",
         "postcss-preset-env": "^3.4.0",
+        "precss": "^3.1.2",
         "purgecss-webpack-plugin": "^1.1.0",
         "style-loader": "^0.21.0",
         "tailwindcss": "^0.5.1",