Bump xo from 0.18.2 to 0.21.1

[dependabot-preview]

Bumps xo from 0.18.2 to 0.21.1.

Release notes

Sourced from xo's releases.

v0.21.1

Fix space/useTabs conflict message with Prettier. xojs/xo@36f7f38

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. xojs/xo@f67ff58
• Disable unicorn/number-literal-case when using Prettier to avoid conflict. xojs/xo@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

• valid-jsdoc
• promise/no-new-statics
• promise/valid-params
• import/no-self-import
• import/no-useless-path-segments

Removed rules

• import/prefer-default-export

v0.20.0

This release is way overdue, so glad to finally have it out! It includes a major ESLint upgrade, huge performance improvements, Prettier support, lots of new rules, and bug fixes.

The project was recently moved to a GitHub organization, and we got a new team member, Pierre Vanduynslager ✨

We now also have configs for TypeScript (using tslint) and CSS & Sass (using stylelint). And don't forget, we already have a config for React.

Many of the new rules in this release are from the eslint-plugin-unicorn plugin, which could use some contributions.

Highlights

• Upgraded to ESLint 4. xojs/xo@a11e288
• Added optional Prettier support. xojs/xo@fd89175
• Improved performance. xojs/xo@552cbb1
• Now toggles rules based on the engines field in package.json. xojs/xo@0d18368
• Disabled linebreak-style rule on Windows. xojs/eslint-config-xo@3f81796
• Made the spaced-comment rule more lenient. xojs/eslint-config-xo@e4f1f36
• Now allows _ as argument name in the no-unused-vars rule. xojs/eslint-config-xo@dda366b
• The --open flag now opens errors first and not warnings. xojs/xo@6f6a606
• Removed deprecated --compact CLI flag. xojs/xo@652a6e5
• Excluded babel-register and babel-polyfill from the no-unassigned-import rule. xojs/xo@70d6ab4
• Sets ecmaVersion to 2018. 9859dfb

New rules

... (truncated)

Commits

• a28625a 0.21.1
• 36f7f38 Fix space/useTabs conflict message (#327)
• 0765998 0.21.0
• 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)
• Additional commits viewable in compare view

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