fix(package): update postcss-advanced-variables to version 2.1.0

Closes #46

Author: greenkeeper[bot]

package.json

@@ -43,7 +43,7 @@
     "lodash": "4.16.6",
     "marked": "0.3.6",
     "minimist": "1.2.0",
-    "postcss-advanced-variables": "1.2.2",
+    "postcss-advanced-variables": "2.1.0",
     "postcss-loader": "1.1.0",
     "prettyjson": "1.1.3",
     "react": "^15.3.2",