Update mem in group website to the latest version � (#635)

Summary:
## The dependency [mem](https://github.com/sindresorhus/mem) was updated from `5.1.1` to `6.0.0`.
This version is **not covered** by your **current version range**.

If you don’t accept this pull request, your project will work just like it did before. However, you might be missing out on a bunch of new features, fixes and/or performance improvements from the dependency update.

 ---

**Publisher:** [sindresorhus](https://www.npmjs.com/~sindresorhus)
**License:** MIT

[Find out more about this release](https://github.com/sindresorhus/mem).

 ---

<details>
  <summary>FAQ and help</summary>

  There is a collection of [frequently asked questions](https://greenkeeper.io/faq.html). If those don’t help, you can always [ask the humans behind Greenkeeper](https://github.com/greenkeeperio/greenkeeper/issues/new).
</details>

 ---

Your [Greenkeeper](https://greenkeeper.io) bot 🌴
Pull Request resolved: https://github.com/facebook/flipper/pull/635

Reviewed By: jknoxville

Differential Revision: D18449137

Pulled By: passy

fbshipit-source-id: 2ca358574ef710e0113e092d2d887ef2c2ac8047

static/package.json

@@ -16,7 +16,7 @@
     "@babel/preset-react": "^7.0.0",
     "expand-tilde": "^2.0.2",
     "fix-path": "^2.1.0",
-    "mem": "^5.1.1",
+    "mem": "^6.0.0",
     "metro": "^0.57.0",
     "mkdirp": "^0.5.1",
     "p-map": "^3.0.0",

static/yarn.lock

@@ -2189,14 +2189,13 @@ mem@^1.1.0:
   dependencies:
     mimic-fn "^1.0.0"
 
-mem@^5.1.1:
-  version "5.1.1"
-  resolved "https://registry.yarnpkg.com/mem/-/mem-5.1.1.tgz#7059b67bf9ac2c924c9f1cff7155a064394adfb3"
-  integrity sha512-qvwipnozMohxLXG1pOqoLiZKNkC4r4qqRucSoDwXowsNGDSULiqFTRUF05vcZWnwJSG22qTsynQhxbaMtnX9gw==
+mem@^6.0.0:
+  version "6.0.0"
+  resolved "https://registry.yarnpkg.com/mem/-/mem-6.0.0.tgz#f79bb110b90b688a2d1468566e66a911794abee5"
+  integrity sha512-1zHBKMg0Xd4yw3EQju6cjJiNtPomak7aNkuJx19QihMco09icTTsLZtVvxfxBxQH/NNvjtA1skR9lDlvkdW46g==
   dependencies:
     map-age-cleaner "^0.1.3"
-    mimic-fn "^2.1.0"
-    p-is-promise "^2.1.0"
+    mimic-fn "^3.0.0"
 
 merge-stream@^1.0.1:
   version "1.0.1"
@@ -2448,10 +2447,10 @@ mimic-fn@^1.0.0:
   resolved "https://registry.yarnpkg.com/mimic-fn/-/mimic-fn-1.2.0.tgz#820c86a39334640e99516928bd03fca88057d022"
   integrity sha512-jf84uxzwiuiIVKiOLpfYk7N46TSy8ubTonmneY9vrpHNAnp0QBt2BxWV9dO3/j+BoVAb+a5G6YDPW3M5HOdMWQ==
 
-mimic-fn@^2.1.0:
-  version "2.1.0"
-  resolved "https://registry.yarnpkg.com/mimic-fn/-/mimic-fn-2.1.0.tgz#7ed2c2ccccaf84d3ffcb7a69b57711fc2083401b"
-  integrity sha512-OqbOk5oEQeAZ8WXWydlu9HJjz9WVdEIvamMCcXmuqUYjTknH/sqsWvhQ3vgwKFRR1HpjvNBKQ37nbJgYzGqGcg==
+mimic-fn@^3.0.0:
+  version "3.0.0"
+  resolved "https://registry.yarnpkg.com/mimic-fn/-/mimic-fn-3.0.0.tgz#76044cfa8818bbf6999c5c9acadf2d3649b14b4b"
+  integrity sha512-PiVO95TKvhiwgSwg1IdLYlCTdul38yZxZMIcnDSFIBUm4BNZha2qpQ4GpJ++15bHoKDtrW2D69lMfFwdFYtNZQ==
 
 minimatch@3.0.4, minimatch@^3.0.4:
   version "3.0.4"
@@ -2754,11 +2753,6 @@ p-finally@^1.0.0:
   resolved "https://registry.yarnpkg.com/p-finally/-/p-finally-1.0.0.tgz#3fbcfb15b899a44123b34b6dcc18b724336a2cae"
   integrity sha1-P7z7FbiZpEEjs0ttzBi3JDNqLK4=
 
-p-is-promise@^2.1.0:
-  version "2.1.0"
-  resolved "https://registry.yarnpkg.com/p-is-promise/-/p-is-promise-2.1.0.tgz#918cebaea248a62cf7ffab8e3bca8c5f882fc42e"
-  integrity sha512-Y3W0wlRPK8ZMRbNq97l4M5otioeA5lm1z7bkNkxCka8HSPjR0xRWmpCmc9utiaLP9Jb1eD8BgeIxTW4AIF45Pg==
-
 p-limit@^1.1.0:
   version "1.3.0"
   resolved "https://registry.yarnpkg.com/p-limit/-/p-limit-1.3.0.tgz#b86bd5f0c25690911c7590fcbfc2010d54b3ccb8"