Linting error due to "useless path segments"

[HexagonSun]

When trying to run the tests with a fresh install of "uppercamelcase" & its dependencies, the tests fail due to a linting error:

uppercamelcase$ npm run test

> uppercamelcase@3.0.0 test /tmp/uppercamelcase
> xo && ava
  ...
test.js:2:1
✖  2:1   Do not reference the index file directly       unicorn/import-index
✖  2:15  Useless path segments for "./", should be "."  import/no-useless-path-segments
  ...

npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! uppercamelcase@3.0.0 test: `xo && ava`
npm ERR! Exit status 1

Used versions:

Node v9.4.0
NPM 5.6.0
xo: 0.21.0
ava: 0.25.0

[HexagonSun]

I've created PR #5 for this. Together with PR#3 (for issue #2) this allows the tests run to completion.

$ npm run test

> uppercamelcase@3.0.0 test /tmp/uppercamelcase
> xo && ava


  1 passed

[SamVerschueren]

Just file one PR with all the linting fixes. This also requires us to drop support for Node.js 4 which I'm fine with. So edit .travis.yaml as well and bump the engines field in package.json.