downgrade packages because lib:css wasn't building right

Author: dmt0

package.json

@@ -43,8 +43,8 @@
     "babel-preset-react": "^6.24.1",
     "babel-preset-stage-2": "^6.24.1",
     "babel-traverse": "^6.26.0",
-    "css-loader": "^1.0.0",
-    "cssnano": "^4.1.0",
+    "css-loader": "^0.28.11",
+    "cssnano": "^3.10.0",
     "enzyme": "^3.1.0",
     "enzyme-adapter-react-16": "^1.0.4",
     "eslint": "^5.4.0",
@@ -59,9 +59,9 @@
     "jest-cli": "^23.5.0",
     "mkdirp": "^0.5.1",
     "node-sass": "^4.7.2",
-    "postcss": "^7.0.2",
+    "postcss": "^6.0.23",
     "postcss-combine-duplicated-selectors": "^6.0.2",
-    "postcss-custom-properties": "^7.0.0",
+    "postcss-custom-properties": "^6.3.1",
     "postcss-remove-root": "^0.0.2",
     "prettier": "1.14.2",
     "react": "^16.0.0",