Update fs-extra requirement to ^6.0.0 (#185)

Updates the requirements on [fs-extra](https://github.com/jprichardson/node-fs-extra) to permit the latest version.
- [Release notes](https://github.com/jprichardson/node-fs-extra/releases)
- [Changelog](https://github.com/jprichardson/node-fs-extra/blob/master/CHANGELOG.md)
- [Commits](https://github.com/jprichardson/node-fs-extra/commits/6.0.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

package.json

@@ -48,7 +48,7 @@
   },
   "dependencies": {
     "bluebird": "^3.0.6",
-    "fs-extra": "^5.0.0",
+    "fs-extra": "^6.0.0",
     "glob-all": "^3.1.0",
     "is-wsl": "^1.1.0",
     "jszip": "^3.1.0",