TASK: Update dependency babel-eslint to v9

[renovate[bot]]

This Pull Request updates dependency babel-eslint (source) from v8.2.6 to v9.0.0

Release Notes

v9.0.0

Compare Source

v9.0.0

We've released v7: https://twitter.com/left_pad/status/1034204330352500736, so this just updates babel-eslint to use those versions internally. That in itself doesn't break anything but:

• Babel now supports the new decorators proposal by default, so we need to switch between the new and the old proposal. This is a breaking change.

To enable the legacy decorators proposal users should add a specific parser option:

{
  parserOptions: {
    ecmaFeatures: {
      legacyDecorators: true
    }
  }
}

• Babel removed the support for Node 4 , so I propagated that here.

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