PF4 Dropdown typescript issues (regression)

[dlabrecq]

I installed the latest react-core package and the typescript issues previously fixed have cropped back in again. In particular, with the toggle property.

I believe the change below caused the regression.
#900

Typescript errors:

My Dropdown usage:

[dmiller9911]

https://github.com/patternfly/patternfly-react/blob/master/packages/patternfly-4/react-core/src/components/Dropdown/Dropdown.d.ts#L14 that should be ReactNode. Could make it potentially more strict with ReactElement, but I don't see much value in that.