fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-POSTCSS-5926692

Author: snyk-bot

package.json

@@ -24,7 +24,7 @@
     "react-scripts": "./bin/react-scripts.js"
   },
   "dependencies": {
-    "autoprefixer": "6.3.7",
+    "autoprefixer": "10.0.0",
     "babel-core": "6.10.4",
     "babel-eslint": "6.1.2",
     "babel-loader": "6.2.4",
@@ -37,7 +37,7 @@
     "babel-preset-react": "6.11.1",
     "chalk": "1.1.3",
     "cross-spawn": "4.0.0",
-    "css-loader": "0.23.1",
+    "css-loader": "5.0.0",
     "eslint": "3.1.1",
     "eslint-loader": "1.4.1",
     "eslint-plugin-import": "1.10.3",
@@ -48,7 +48,7 @@
     "html-webpack-plugin": "2.22.0",
     "json-loader": "0.5.4",
     "opn": "4.0.2",
-    "postcss-loader": "0.9.1",
+    "postcss-loader": "4.0.0",
     "rimraf": "2.5.3",
     "semver": "^5.3.0",
     "style-loader": "0.13.1",