TypeScript error when using node 14 type definitions

I currently have to keep my `@types/node` dev dependency at 12.x in order to avoid the following:

```
C:/myproject/node_modules/modbus-stream/types/index.d.ts(99,26): error TS2689: Cannot extend an interface 'NodeJS.EventEmitter'. Did you mean 'implements'?
TypeScript: 1 semantic error
```