Fixed typo in concepts.ngdoc

[markau]

The service is in finance2.js but the doc references finance.js

[mary-poppins]

Thanks for the PR! Please check the items below to help us merge this faster. See the contributing docs for more information.

• Uses the issue template (#7470)

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Then, update the pull request with git push -f.

Thanks again for your help!

[mary-poppins]

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