Dropdown component should not use deprecated "componentWillUpdate" lifecycle method

[broneks]

Problem:
componentWillUpdate is deprecated and will eventually be removed following React v17.

See warning message here:

Suggestion:
It would be wise to switch this method for a componentDidMount being that this block of code is adding event listeners which don't need to be re-added on/before every update.

react-multi-select/src/dropdown.js

Line 32 in 19a6d69

componentWillUpdate() {

[rajan-gith]

how to fix this warning

[frealv]

This is still an issue.

[broneks]

Duplicated by: #70