style(discover): increase width of source card

- Adjust the width of the source card from 120 to 150 units

Author: fulleni

lib/discover/view/discover_page.dart

@@ -189,7 +189,7 @@ class _SourceCard extends StatelessWidget {
     final theme = Theme.of(context);
 
     return SizedBox(
-      width: 120,
+      width: 150,
       child: Card(
         clipBehavior: Clip.antiAlias,
         child: InkWell(