[BUG] Error: Cannot find module 'tslib'

Describe the bug

Hi! First of all: Thank you for providing this great library. With the update to the latest patch version of fast-csv, I started to get some error messages when trying to import the library:

Error: Cannot find module 'tslib'
     at Function.Module._resolveFilename (internal/modules/cjs/loader.js:636:15)
     at Function.Module._load (internal/modules/cjs/loader.js:562:25)
     at Module.require (internal/modules/cjs/loader.js:692:17)
     at require (internal/modules/cjs/helpers.js:25:18)
     at Object.<anonymous> xxx/node_modules/@fast-csv/format/build/src/index.js:4:17)
     at Module._compile (internal/modules/cjs/loader.js:778:30)
     at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
     at Module.load (internal/modules/cjs/loader.js:653:32)
     at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
     at Function.Module._load (internal/modules/cjs/loader.js:585:3)

I assume, this is down to the following change in your tsconfig: https://github.com/C2FO/fast-csv/commit/666800653811b54bd32c5afb59b9ef146ac7828e#diff-17d19956339a21e53394cda05f5a6cc3R9

You added "importHelpers": true which will (as I found out) Import emit helpers from 'tslib'. Yet, tslib is not defined as a dependency, so I assume this compiler option emits some code that fails at runtime if the dependency is not present.

Parsing or Formatting?

• Formatting
• Parsing

To Reproduce

I’ll update with a mwe, currently building one

Expected behavior

Importing the library should be possible without having to require tslib myself explicitly.

Desktop (please complete the following information):

• OS: Windows
• OS Version 10
• Node Version 10.18.1

(But also my Jenkins, which runs on Linux, but I don’t know exact version there)