fix(package): update fs-extra to version 8.1.0

Closes #331

Author: greenkeeper[bot]

package.json

@@ -15,7 +15,7 @@
     "cli-truncate": "^1.1.0",
     "emphasize": "^2.0.0",
     "fancy-log": "^1.3.3",
-    "fs-extra": "^7.0.1",
+    "fs-extra": "^8.1.0",
     "in-gfw": "^1.2.0",
     "is-windows": "^1.0.2",
     "js-yaml": "^3.12.0",