fix: fix line point color style (#174)

Author: leondt1

bindings/gpt-vis-ssr/__tests__/line.spec.ts

@@ -103,6 +103,11 @@ describe('SSR render', () => {
       group: true,
       axisXTitle: 'Month',
       axisYTitle: 'Temperature',
+      style: {
+        backgroundColor: '#aaa',
+        lineWidth: 4,
+        palette: PALETTE,
+      },
     });
 
     expect(vis.toBuffer()).toImageEqual('__tests__/snapshot', 'line-grouped');

bindings/gpt-vis-ssr/__tests__/snapshot/line-grouped.png

@@ -98,7 +98,11 @@ export async function Line(options: LineOptions) {
           shape: 'point',
           ...(lineWidth ? { size: lineWidth * 1.2 } : {}),
         },
-        style: { fill: 'white', lineWidth: 1, ...(hasPalette ? { stroke: palette[0] } : {}) },
+        style: {
+          fill: 'white',
+          lineWidth: 1,
+          ...(hasPalette && !hasGroupField ? { stroke: palette[0] } : {}),
+        },
       },
     ],
     scale: {