Add forced-mode param in the signature header request

[papegaill]

There is a param to force request mode between 'real' or 'paper' on your account, see:
https://github.com/3commas-io/3commas-official-api-docs#api-modesreal-or-paper

Goal is to have possibility to force this option.

[rentorm]

thanks for introducing this change! It's merged and published now in v1.1.0

[richjenks]

@rentorm is it desirable that the forcedMode option is mandatory?

The readme explicitly states that it's optional but you get an error if it's omitted.

I pointed this out in the PR and wonder if it should be optional because that's the default behaviour of the 3commas API.

Thoughts?

[rentorm]

thanks @richjenks and @papegaill I've published new release with merge from #21