fix(test): update @types/webpack

[IlyaSurmay]

Fixes this error during ng test

Error: 
C:/Source/ngx-bootstrap/node_modules/@types/webpack/index.d.ts (530,28): Type 'typeof "C:/Source/ngx-bootstrap/node_modules/@types/tapable/index"' is not a constructor function type.,
C:/Source/ngx-bootstrap/node_modules/@types/webpack/index.d.ts (557,42): Type 'typeof "C:/Source/ngx-bootstrap/node_modules/@types/tapable/index"' is not a constructor function type.,
C:/Source/ngx-bootstrap/node_modules/@types/webpack/index.d.ts (573,46): Namespace '"C:/Source/ngx-bootstrap/node_modules/@types/tapable/index"' has no exported member 'Plugin'.,
C:/Source/ngx-bootstrap/node_modules/@types/webpack/index.d.ts (577,53): Namespace '"C:/Source/ngx-bootstrap/node_modules/@types/tapable/index"' has no exported member 'Plugin'.

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