Heisenbug with LocalStorageTemp in Travis

[dpordomingo]

Heisenbug with LocalStorageTemp in Travis (ie https://travis-ci.org/src-d/code-annotation/jobs/349738180)

Frequency not calculated, but can be around 1/10

If the build is restarted, it can dissappear.

make test-frontend
[...]
react-app-rewired test --env=jsdom
 FAIL  src/state/features.test.js
  ● Test suite failed to run
    EEXIST: file already exists, mkdir '/home/travis/gopath/src/github.com/src-d/code-annotation/localStorageTemp'
      at Object.fs.mkdirSync (fs.js:885:18)
      at LocalStorage.Object.<anonymous>.LocalStorage._init (node_modules/node-localstorage/LocalStorage.js:151:12)
      at new LocalStorage (node_modules/node-localstorage/LocalStorage.js:121:12)
      at Object.<anonymous> (setupJest.js:5:23)
      at handle (node_modules/worker-farm/lib/child/index.js:44:8)