Minor linting updates

[lemonmade]

This PR makes a few small JavaScript linting/ styleguide updates:

• Made it so that require-flow allows @flow to appear in a line comment (which is apparently allowed now).
• Removed the requirement to omit the braces for arrow functions that have only a return statement and updated the guidance for them to suggest (but not require) omitting the braces for simple return-only arrow functions.
• Turned off linting rules that enforced sorting of properties in React components. This was annoying in my experience and doesn't have the granularity to make it work well with class properties.
• Turned off a rule that required you to use a default export when your module exports only one identifier. IMO some modules make more sense as groups of named exports (usually utility-like things), even if you currently only have one export from that group.

Thoughts? @GoodForOneFare @bouk @tessalt @Shopify/fed

[GoodForOneFare]

Should .filter be on a new line?

[GoodForOneFare]

👍 LGTM.

[bouk]

🔥 this rule 👍

[tessalt]

can we get this released?

[lemonmade]

@tessalt 13.0.0 released with all the linting changes, let me know if you have nay issues!