Fix lastModified Filter

[Jdubrick]

What does this PR do?:

Summarize the changes. Are any stacks or samples added or updated?
This PR aims to fix the issue described in the linked issue below regarding stacks showing the default Go time.Time value. The stack and version vars in the generation script were flipped, resulting in the parsing from index/generator to not be able to find the resulting stacks and issuing the default date as a result.

Which issue(s) this PR fixes:

Link to github issue(s)
fixes devfile/api#1610

PR acceptance criteria:

• Contributing guide
  Have you read the devfile registry contributing guide and followed its instructions?
• Test automation
  Does this repository's tests pass with your changes?
• Documentation
  Does any documentation need to be updated with your changes?
• Check Tools Provider
  Have you tested the changes with existing tools, i.e. Odo, Che, Console? (See devfile registry contributing guide on how to test changes)

How to test changes / Special notes to the reviewer:

Run bash .ci/build.sh and launch the registry and then hit /v2index to see lastModified dates are not the default anymore

[maysunfaisal]

/lgtm

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Jdubrick, maysunfaisal

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