Select does not stretch to fit the sized container

[moshie]

When setting the inputSize prop on the Dropdown field the select does not change size.

https://github.com/zopaUK/react-components/blob/59a922d5d9d556d2fa1a34ee13184ceb0f194258/src/components/molecules/DropdownField/DropdownField.tsx#L44-L53