Use the latest stable versions of cssnano and postcss

Author: frenzzy

package.json

@@ -28,9 +28,9 @@
     "webpack": "^4.0.0"
   },
   "dependencies": {
-    "cssnano": "^4.0.0-rc.2",
-    "cssnano-preset-default": "^4.0.0-rc.2",
-    "postcss": "^6.0.19"
+    "cssnano": "^4.0.0",
+    "cssnano-preset-default": "^4.0.0",
+    "postcss": "^7.0.0"
   },
   "devDependencies": {
     "autoprefixer": "^8.0.0",