"isPlainObject.isPlainObject is not a function" error on some component

[maxime-rainville]

Some components (e.g.: Toast) fail with this error: isPlainObject.isPlainObject is not a function

https://silverstripe.github.io/silverstripe-pattern-lib/?knob-message=Hello%20World&knob-status=default&knob-pill=true&knob-text=The%20quick%20brown%20fox%20jumps%20over%20the%20lazy%20dog&knob-type=info&knob-actions=0&selectedKind=Admin%2FToasts&selectedStory=Single&full=0&addons=1&stories=1&panelRight=0&addonPanel=storybook%2Fnotes%2Fpanel

Pull request

• BUG Add missing dependency to build pattern library silverstripe-admin#1291