Update xo to the latest version 🚀

Version 0.21.0 of xo was just published.

Dependency	`xo`
Current Version	0.20.3
Type	devDependency

The version 0.21.0 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.

It might be worth looking into these changes and trying to get this project onto the latest version of xo.

If you have a solid test suite and good coverage, a passing build is a strong indicator that you can take advantage of these changes directly by merging the proposed change into your project. If the build fails or you don’t have such unconditional trust in your tests, this branch is a great starting point for you to work on the update.

Release Notes

v0.21.0

Highlights

Dropped support for Node.js 4 and 5 as they reached end of life. Node.js 6 is the minimum required version.
Upgrade to Prettier 1.12.1.
The default value for trailingComma Prettier option is now none. f67ff58
Disable unicorn/number-literal-case when using Prettier to avoid conflict. 4fd6991
Ignore prettier-ignore comments in capitalized-comments rule. xojs/eslint-config-xo@6e417ff
Fix missed detection of incorrect indentation with indent rule. xojs/eslint-config-xo@145993e
Allow named function in prefer-arrow-callback. xojs/eslint-config-xo@bda02cb

New rules

Removed rules

import/prefer-default-export

Commits

The new version differs by 8 commits.

b633e92 Do not override default options with absent CLI flags (#316)
cec0853 Update plugins and add some new rules
d1eb47c Require Node.js 6
6254110 GitHub now natively supports SVG
4fd6991 Disable number-literal-case rule when using Prettier (#311)
7190640 Remove import/prefer-default-export rule
f67ff58 Default Prettier trailingComma conf to none (#305)
11c35c8 Upgrade prettier to last version (#306)

See the full diff

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semantic-release / travis-deploy-once