fix: use xDAI and xBZZ on Gnosis chain (#454)

* fix: use xDAI on Gnosis chain

* fix: rename BZZ to xBZZ when on Gnosis chain

* fix: replace MINIMUM_xDAI with MINIMUM_XDAI

* fix: update xdai links to correct gnosis chain urls

src/pages/top-up/TopUpProgressIndicator.tsx

@@ -6,5 +6,5 @@ interface Props {
 }
 
 export function TopUpProgressIndicator({ index }: Props): ReactElement {
-  return <ProgressIndicator index={index} steps={['Buy xDAI', 'Swap BZZ']} />
+  return <ProgressIndicator index={index} steps={['Buy xDAI', 'Swap xBZZ']} />
 }