fix(runtime-dom): support mounting app to svg container (#2929)

fix #2926

packages/runtime-dom/__tests__/createApp.spec.ts

@@ -0,0 +1,15 @@
+import { createApp, h } from '../src'
+
+describe('createApp for dom', () => {
+  // #2926
+  test('mount to SVG container', () => {
+    const root = document.createElementNS('http://www.w3.org/2000/svg', 'svg')
+    createApp({
+      render() {
+        return h('g')
+      }
+    }).mount(root)
+    expect(root.children.length).toBe(1)
+    expect(root.children[0] instanceof SVGElement).toBe(true)
+  })
+})