fix(Dropdown): retrieve both state and props for displayMenu to trigger rerender

[sun-tea]

• Feature
• Fix
• Enhancement

Brief

displayMenu did not seem to trigger rerender despite being updated in the internal state, turns out I think it's because the way the variable was being retrieved would not trigger a rerender.

Todo - Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.