Update Dart sample to latest Dart server template

[mit-mit]

Update all Dart sample files to follow the latest Dart server template (dart create -t server-shelf).

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[knative-prow]

Welcome @mit-mit! It looks like this is your first PR to knative/docs 🎉

[knative-prow]

Hi @mit-mit. Thanks for your PR.

I'm waiting for a knative member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[mit-mit]

@jonasfj can you please review?

[mit-mit]

@jonasfj is on vacation; @kevmoo can you LGTM?

[hrishikesh-kadam]

Hi @mit-mit!
dart word seems to be missing in the command.

I came to this PR by traversing the following path -

1. https://www.cloudskillsboost.google/course_sessions/1402704/labs/187125
   The hyperlink at the end of Task 2

2. https://cloud.google.com/run/docs/quickstarts
   Click "Build and deploy a service in other languages"

3. https://cloud.google.com/run/docs/quickstarts/build-and-deploy/deploy-service-other-languages
   Write the sample application -> Two Dart hyperlink

So, someone from the Cloud Team might need to update the above hyperlinks once this goes live.

[mit-mit]

dart word seems to be missing in the command.

oh, good catch, fixed now

[knative-prow]

@kevmoo: changing LGTM is restricted to collaborators

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[abrennan89]

/ok-to-test
/lgtm

[abrennan89]

/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: abrennan89, kevmoo, mit-mit

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[abrennan89]

@mit-mit any errors reported will need to be fixed before this can merge: https://github.com/knative/docs/runs/7770884752?check_suite_focus=true

[mit-mit]

@abrennan89 I fixed the test issue

[abrennan89]

/lgtm