Fix toggle switch bug when Flipper's width is small

Summary:
Bug:

{F214979227}

Reviewed By: passy

Differential Revision: D17763781

fbshipit-source-id: 21890caee796ac0df6f39e618a762c44955dd647

src/ui/components/ToggleSwitch.tsx

@@ -19,6 +19,7 @@ export const StyledButton = styled('div')((props: {toggled: boolean}) => ({
   borderRadius: '100px',
   position: 'relative',
   marginLeft: '15px',
+  flexShrink: 0,
   '&::after': {
     content: '""',
     position: 'absolute',