added purgecss and cssnano

package.json

@@ -64,6 +64,7 @@
     "@babel/polyfill": "^7.0.0",
     "@babel/preset-env": "^7.1.0",
     "@dannycoates/webpack-dev-server": "^3.1.4",
+    "@fullhuman/postcss-purgecss": "^1.1.0",
     "@mattiasbuelens/web-streams-polyfill": "0.1.0",
     "asmcrypto.js": "^2.3.2",
     "babel-loader": "^8.0.4",
@@ -76,6 +77,7 @@
     "cross-env": "^5.2.0",
     "css-loader": "^1.0.0",
     "css-mqpacker": "^7.0.0",
+    "cssnano": "^4.1.7",
     "eslint": "^5.6.1",
     "eslint-plugin-mocha": "^5.2.0",
     "eslint-plugin-node": "^7.0.1",
@@ -97,8 +99,6 @@
     "nanotiming": "^7.3.1",
     "npm-run-all": "^4.1.3",
     "nyc": "^13.0.1",
-    "postcss-cssnext": "^3.1.0",
-    "postcss-import": "^12.0.0",
     "postcss-loader": "^3.0.0",
     "prettier": "^1.14.3",
     "proxyquire": "^2.1.0",