feat(ui):替换watch 预览背景图片

@@ -43,7 +43,7 @@ class WatchFacePreview extends StatelessWidget {
 
   Size get _previewSize {
     if (type == WatchFacePreviewType.singleMedium) {
-      return Size(134, 160);
+      return Size(139, 160);
     }
     return Size(120, 136);
   }
@@ -74,9 +74,9 @@ class WatchFacePreview extends StatelessWidget {
             children: [
               Image(
                 image: AssetImage(_backgroundAsset(context)),
-                width: size.width,
+                // width: size.width,
                 height: size.height,
-                fit: BoxFit.fitWidth,
+                fit: BoxFit.fitHeight,
               ),
               _buildThemeImages(),
             ],