message: Use SystemStyleObject from in TS sx prop typings
diff: declare module '@primer/components' {
  type Omit<T, K> = Pick<T, Exclude<keyof T, K>>
  import * as StyledSystem from 'styled-system'
  + import {SystemStyleObject} from '@styled-system/css'
  import * as StyledComponents from 'styled-components'
  import * as History from 'history'
  @@ -8,7 +9,7 @@ declare module '@primer/components' {
  as?: React.ReactType
  className?: string
  css?: string
  - sx?: object
  + sx?: SystemStyleObject
  title?: string
  // NOTE(@mxstbr): Necessary workaround to make <Component as={Link} to="/bla" /> work
  to?: History.LocationDescriptor
  