Update to latest dart version

[akashgk]

Welcome to Dart community

Describe your change:

Upgrade to latest dart version

Checklist:

• [*] I have read CONTRIBUTING.md.
• [*] This pull request is all my own work -- I have not plagiarized.
• [*] I know that pull requests will not be merged if they fail the automated tests.
• [*] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• [*] All new Dart files are placed inside an existing directory.
• [*] All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• [*] If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.