Update dependency async to v2.6.4

[mend-for-github-com[bot]]

This PR contains the following updates:

Package	Type	Update	Change
async (source)	devDependencies	patch	2.6.1 -> 2.6.4

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Release Notes

caolan/async (async)

### [`v2.6.4`](https://redirect.github.com/caolan/async/compare/v2.6.3...v2.6.4) [Compare Source](https://redirect.github.com/caolan/async/compare/v2.6.3...v2.6.4) ### [`v2.6.3`](https://redirect.github.com/caolan/async/compare/v2.6.2...v2.6.3) [Compare Source](https://redirect.github.com/caolan/async/compare/v2.6.2...v2.6.3) ### [`v2.6.2`](https://redirect.github.com/caolan/async/compare/v2.6.1...v2.6.2) [Compare Source](https://redirect.github.com/caolan/async/compare/v2.6.1...v2.6.2)

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