fix: upgrade cssnano from 4.0.5 to 4.1.10

Snyk has created this PR to upgrade cssnano from 4.0.5 to 4.1.10.

See this package in NPM:
https://www.npmjs.com/package/cssnano

See this project in Snyk:
https://app.snyk.io/org/luisalejandro/project/709c2db5-08fb-4d5f-88a4-53be6eecb157?utm_source=github&utm_medium=upgrade-pr

Author: snyk-bot

package-lock.json

@@ -69,7 +69,7 @@
     "browserify": "16.2.2",
     "browserify-shim": "3.8.14",
     "css-mqpacker": "7.0.0",
-    "cssnano": "4.0.5",
+    "cssnano": "4.1.10",
     "del": "3.0.0",
     "eslint": "5.4.0",
     "eslint-config-standard": "12.0.0-alpha.0",