Fix prefetcher types

Reviewed By: passy

Differential Revision: D17164305

fbshipit-source-id: edc52a0708e2a46a3fe2aa9752fd94fa0b1909be

package.json

@@ -51,6 +51,7 @@
   "devDependencies": {
     "@jest-runner/electron": "^2.0.1",
     "@types/deep-equal": "^1.0.1",
+    "@types/fs-extra": "^8.0.0",
     "@types/invariant": "^2.2.30",
     "@types/jest": "^24.0.16",
     "@types/lodash.debounce": "^4.0.6",

yarn.lock

@@ -1077,6 +1077,13 @@
   resolved "https://registry.yarnpkg.com/@types/events/-/events-3.0.0.tgz#2862f3f58a9a7f7c3e78d79f130dd4d71c25c2a7"
   integrity sha512-EaObqwIvayI5a8dCzhFrjKzVwKLxjoG9T6Ppd5CEo07LRKfQ8Yokw54r5+Wq7FaBQ+yXRvQAYPrHwya1/UFt9g==
 
+"@types/fs-extra@^8.0.0":
+  version "8.0.0"
+  resolved "https://registry.yarnpkg.com/@types/fs-extra/-/fs-extra-8.0.0.tgz#d3e2c313ca29f95059f198dd60d1f774642d4b25"
+  integrity sha512-bCtL5v9zdbQW86yexOlXWTEGvLNqWxMFyi7gQA7Gcthbezr2cPSOb8SkESVKA937QD5cIwOFLDFt0MQoXOEr9Q==
+  dependencies:
+    "@types/node" "*"
+
 "@types/glob@^7.1.1":
   version "7.1.1"
   resolved "https://registry.yarnpkg.com/@types/glob/-/glob-7.1.1.tgz#aa59a1c6e3fbc421e07ccd31a944c30eba521575"