[vscode-concourse] complains about vars in task step

[pascalwhoop]

Docs of concourse:
https://concourse-ci.org/task-step.html#task-step-vars

[kdvolder]

The fix should now be available from snapshot build. A vscode vsix file can be downloaded here:

http://dist.springsource.com/snapshot/STS4/nightly-distributions.html