```

build(devcontainer): 修复Dockerfile路径配置

更新devcontainer.json中的Dockerfile路径，从相对路径".devcontainer/Dockerfile"
修改为"Dockerfile"，以确保正确的构建上下文。
```

day01/devcontainer/.devcontainer/devcontainer.json

@@ -1,7 +1,7 @@
 {
   "name": "Go Dev Container (demo)",
   "build": {
-    "dockerfile": ".devcontainer/Dockerfile"
+    "dockerfile": "Dockerfile"
   },
   "remoteUser": "vscode",
   "workspaceFolder": "/workspaces/${localWorkspaceFolderBasename}",