Fix build error after rebuilding lockfile

[claabs]

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Description

Generating a new yarn.lock, or npm installing installs of @types/clean-webpack-plugin@0.1.3 which breaks the gulp build script. This PR pins @types/clean-webpack-plugin@0.1.2.

❤️ Thank you!

[Dabolus]

LGTM, thanks!

P.S. Don't worry about the failed CI, it is still buggy