Bump client's eslint; fix new linting errors

[drewrey]

Bump client's eslint; fix new linting errors

• Avoid object as a PropType
• Specify a default PropType for non-required props
• Make other props required
• Ignore no-array-index-key until poem lines have DB ids.
• Remove parens from one-argument arrow functions
• Add dangling commas except in functions.
• Remove un-used session from SessionSortablePoemList
• Bump eslint-related dev-dependencies
• Update yarn.lock

[drewrey]

Weird, I can't respond to your review.

I re-based off master, updated the yarn.lock file, and made these updates to the sortable sessions for eslint:

• found an un-used prop in SessionSortablePoemList
• made a few props required
• removed a few parens around single-var arrow functions.