fix(package): update mkdirp to version 1.0.4

Closes #113

Author: greenkeeper[bot]

package.json

@@ -49,7 +49,7 @@
     "listr": "0.7.0",
     "metalsmith": "^2.2.2",
     "minimatch": "^3.0.3",
-    "mkdirp": "^0.5.1",
+    "mkdirp": "^1.0.4",
     "npm-install-webpack-plugin": "^4.0.4",
     "object-assign": "^4.1.0",
     "ora": "^0.3.0",