fix(deps): update dependency knex to ^0.21.6

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
knex (source)	dependencies	patch	^0.21.5 -> ^0.21.6

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Release Notes

knex/knex

### [`v0.21.6`](https://togithub.com/knex/knex/blob/master/CHANGELOG.md#​0216---27-September-2020) [Compare Source](https://togithub.com/knex/knex/compare/0.21.5...7cfb78d16aa9dcd635c9ae1862837ccd4f507a21) ##### New features: - CLI: New config parameter / CLI flag to prefixing seed filename with timestamp [#​3873](https://togithub.com/knex/knex/issues/3873) - CLI: throw an error when specific seed file cannot be found [#​4011](https://togithub.com/knex/knex/issues/4011) - Warn if whereNot is used with 'in' or 'between' [#​4038](https://togithub.com/knex/knex/issues/4038) ##### Bug fixes: - CLI: Fix double merging of config for migrator [#​4040](https://togithub.com/knex/knex/issues/4040) ##### Typings: - Unify SeedsConfig and SeederConfig [#​4003](https://togithub.com/knex/knex/issues/4003) - Allow string\[] type for directory in SeedsConfig [#​4033](https://togithub.com/knex/knex/issues/4033)

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Codecov Report

Merging #378 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #378   +/-   ##
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  Coverage   27.21%   27.21%           
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  Files          57       57           
  Lines         801      801           
  Branches       62       62           
=======================================
  Hits          218      218           
  Misses        583      583           

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