Bump @types/ioredis from 4.17.7 to 4.17.8 (#473)

Bumps [@types/ioredis](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/HEAD/types/ioredis) from 4.17.7 to 4.17.8.
- [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases)
- [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits/HEAD/types/ioredis)

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