Solution: Remove Supervisor.Spec references

[TylerPachal]

The import statement is not necessary as noted in this issue: https://github.com/quantum-elixir/quantum-core/issues/474

Tested locally with a little dummy project - when the warn: false option was removed it confirmed that the import statement was unused:

warning: unused import Supervisor.Spec
  lib/acme/application.ex:9

[coveralls]

Pull Request Test Coverage Report for Build 7b2bdc651c9215fc758518851d670f3899d75d66-PR-475

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 86.188%

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Totals
Change from base Build eca5ee0c17b2f974c7e9bffb36620a7024c76d03:	0.0%
Covered Lines:	312
Relevant Lines:	362

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💛 - Coveralls