Update xo to version 0.15.1 🚀

[greenkeeperio-bot]

Hello :wave:

:rocket::rocket::rocket:

xo just published its new version 0.15.1, which is not covered by your current version range.

If this pull request passes your tests you can publish your software with the latest version of xo – otherwise use this branch to work on adaptions and fixes.

Happy fixing and merging :palm_tree:

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The new version differs by 14 commits .

• 2afa82d 0.15.1
• 6c09726 pin eslint because of #116
• cc49ed4 test on Node.js 6
• 69fbe68 update code of conduct
• 60fe4d6 clarify theesnextoption
• e3eaf88 0.15.0
• 1eff0bd bump dependencies and other tweaks
• 863b10e fix broken #94
• 9bffce7 Make--spacesapply to JSX (i.e., overrideeslint-config-xo-react). (#94)
• dc35a72 use our new pretty formatter
• eaba33f mention eslint-plugin-xo in the readme
• 0a43304 remove theno-empty-blocksplugin
• 1e4a832 remove jscs-xo from readme
• 5e5c4ef add Team section in readme

See the full diff.

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