chore(docs/options): Typo in `multiple` option

A patch was submitted, but was somehow not up to date with master, so I just
committed solo.

Fixes #1082 for the `multiple` option.
fix(*): Consistent spelling of "canceled".

Conflicts:
	test/unit/submit-validate-cancel.js
docs(quickstart/03-setting_up_server-s3): Tidy

Remove a useless alert and update Node signatureserver link

[skip ci]
Merge branch 'master' into develop

Conflicts:
	docs/api/events.jmd
	docs/api/methods.jmd
	docs/api/options-ui.jmd
	docs/api/options.jmd
	docs/features/cancellable-uploads.jmd
	docs/features/handling-errors.jmd