fix(package): update purgecss to version 2.0.5

Closes #14

Author: greenkeeper[bot]

package.json

@@ -43,7 +43,7 @@
     "rollup-plugin-node-resolve": "^3.3.0"
   },
   "dependencies": {
-    "purgecss": "^1.0.0",
+    "purgecss": "^2.0.5",
     "rollup-pluginutils": "^2.3.0"
   }
 }