Add except-object option to arrow-body-style rules.

[duncanbeevers]

Blockless arrow functions are awesome, but when returning an object literal it's necessary to enclose the return value in parentheses. This rule extension enforces blockless arrow functions excluding cases where the arrow function returns an object literal.

[eslintbot]

Thanks for the pull request, @duncanbeevers! I took a look to make sure it's ready for merging and found some changes are needed:

• The commit summary needs to begin with a tag (such as Fix: or Update:). Please check out our guide for how to properly format your commit summary and update it on this pull request.
• Pull requests with code require an issue to be mentioned at the end of the commit summary, such as (fixes #1234). Please update the commit summary with an issue (file a new issue if one doesn't already exist).

Can you please update the pull request to address these?

(More information can be found in our pull request guide.)

[mention-bot]

By analyzing the blame information on this pull request, we identified @vitorbal, @alberto and @nzakas to be potential reviewers

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[nzakas]

Adding "do not merge" because the issue isn't accepted yet.

[duncanbeevers]

Rebased against fc78e78

[duncanbeevers]

The Travis CI failure against node v0.12 appears to be spurious. I pushed an identical branch to trigger another build and got all green.

[btmills]

I restarted the Travis build for Node.js 0.12.

[alberto]

@duncanbeevers Do you intend to keep working on this?

[duncanbeevers]

@alberto Replied on #5936