added x.svg for close dialogue button

lib/utilities/assets.dart

@@ -13,4 +13,5 @@ class _SVG {
   const _SVG();
 
   String get drifterIcon => "assets/images/logo/drifter_logo_circle.svg";
+  String get x => "assets/images/svg/x.svg";
 }

pubspec.yaml

@@ -64,6 +64,7 @@ flutter:
   # To add assets to your application, add an assets section, like this:
   assets:
     - assets/images/logo/
+    - assets/images/svg/
   #   - images/a_dot_ham.jpeg
 
   # An image asset can refer to one or more resolution-specific "variants", see