Update fs-extra to version 9.0.0 (#315)

Co-authored-by: greenkeeper[bot] <23040076+greenkeeper[bot]@users.noreply.github.com>

Author: greenkeeper[bot]

package.json

@@ -21,7 +21,7 @@
     "chalk": "^3.0.0",
     "chokidar": "^3.3.0",
     "dependency-graph": "^0.9.0",
-    "fs-extra": "^8.1.0",
+    "fs-extra": "^9.0.0",
     "get-stdin": "^7.0.0",
     "globby": "^10.0.1",
     "postcss": "^7.0.0",