calling an extensions command from a vs code task

task.json

{
  "version": "2.0.0",
  "tasks": [
    {
      "label": "plantuml.export",    
      "command": "${command:plantuml.exportCurrent}"
    },    
    {
      "label": "generate diagrams",
      "type": "shell",
      "command": "make diagrams",
      "dependsOrder": "sequence",
      "dependsOn": ["plantuml.export"],
      "group": {
        "kind": "build",
        "isDefault": true
      }
    }
  ]
}