Fix soapboxConfig propType errors

app/soapbox/features/soapbox_config/components/site_preview.js

@@ -52,5 +52,5 @@ export default function SitePreview({ soapbox }) {
 }
 
 SitePreview.propTypes = {
-  soapbox: ImmutablePropTypes.map.isRequired,
+  soapbox: ImmutablePropTypes.record.isRequired,
 };

app/soapbox/features/ui/index.js

@@ -188,7 +188,7 @@ class SwitchingColumnsArea extends React.PureComponent {
     children: PropTypes.node,
     location: PropTypes.object,
     onLayoutChange: PropTypes.func.isRequired,
-    soapbox: ImmutablePropTypes.map.isRequired,
+    soapbox: ImmutablePropTypes.record.isRequired,
     features: PropTypes.object.isRequired,
   };
 
@@ -399,7 +399,7 @@ class UI extends React.PureComponent {
     streamingUrl: PropTypes.string,
     account: PropTypes.object,
     features: PropTypes.object.isRequired,
-    soapbox: ImmutablePropTypes.map.isRequired,
+    soapbox: ImmutablePropTypes.record.isRequired,
     vapidKey: PropTypes.string,
   };