Fixed Typo (#5102)

Summary:
A typo in the settings page has been fixed.

Pull Request resolved: https://github.com/facebook/flipper/pull/5102

Reviewed By: ivanmisuno

Differential Revision: D48948584

Pulled By: passy

fbshipit-source-id: 2469a25d2deb7c6c128f7d88a68fd5d147aad428

desktop/flipper-ui-core/src/chrome/SettingsSheet.tsx

@@ -372,7 +372,7 @@ class SettingsSheet extends Component<Props, State> {
               });
             }}>
             <URLConfigField
-              label="Martkeplace URL"
+              label="Marketplace URL"
               defaultValue={
                 marketplaceURL || 'http://plugin-marketplace.local/get-plugins'
               }